diff --git a/src/d_main.c b/src/d_main.c
index df1180c8..b12dcdbf 100644
--- a/src/d_main.c
+++ b/src/d_main.c
@@ -812,11 +812,6 @@ void D_StartTitle(void)
 	CON_ToggleOff();
 
 	// Reset the palette
-#ifdef HWRENDER
-	if (rendermode == render_opengl)
-		HWR_SetPaletteColor(0);
-	else
-#endif
 	if (rendermode != render_none)
 		V_SetPaletteLump("PLAYPAL");
 }
@@ -1325,7 +1320,7 @@ void D_SRB2Main(void)
 	CONS_Printf("R_Init(): Init SRB2 refresh daemon.\n");
 	R_Init();
 
-	// setting up sound	
+	// setting up sound
 	if (dedicated)
 	{
 		nosound = true;
diff --git a/src/hardware/hw_main.c b/src/hardware/hw_main.c
index b7b8af62..4429bafe 100644
--- a/src/hardware/hw_main.c
+++ b/src/hardware/hw_main.c
@@ -2905,8 +2905,8 @@ static boolean HWR_CheckBBox(fixed_t *bspcoord)
 	py2 = bspcoord[checkcoord[boxpos][3]];
 
 	// check clip list for an open space
-	angle1 = R_PointToAngle(px1, py1) - dup_viewangle;
-	angle2 = R_PointToAngle(px2, py2) - dup_viewangle;
+	angle1 = R_PointToAngle2(dup_viewx>>1, dup_viewy>>1, px1>>1, py1>>1) - dup_viewangle;
+	angle2 = R_PointToAngle2(dup_viewx>>1, dup_viewy>>1, px2>>1, py2>>1) - dup_viewangle;
 
 	span = angle1 - angle2;
 
@@ -4236,6 +4236,9 @@ static void HWR_SplitSprite(gr_vissprite_t *spr)
 	i = 0;
 	temp = FLOAT_TO_FIXED(realtop);
 
+	if (spr->mobj->frame & FF_FULLBRIGHT)
+		lightlevel = 255;
+
 #ifdef ESLOPE
 	for (i = 1; i < sector->numlights; i++)
 	{
@@ -4243,14 +4246,16 @@ static void HWR_SplitSprite(gr_vissprite_t *spr)
 					: sector->lightlist[i].height;
 		if (h <= temp)
 		{
-			lightlevel = *list[i-1].lightlevel;
+			if (!(spr->mobj->frame & FF_FULLBRIGHT))
+				lightlevel = *list[i-1].lightlevel;
 			colormap = list[i-1].extra_colormap;
 			break;
 		}
 	}
 #else
 	i = R_GetPlaneLight(sector, temp, false);
-	lightlevel = *list[i].lightlevel;
+	if (!(spr->mobj->frame & FF_FULLBRIGHT))
+		lightlevel = *list[i].lightlevel;
 	colormap = list[i].extra_colormap;
 #endif
 
@@ -4265,7 +4270,8 @@ static void HWR_SplitSprite(gr_vissprite_t *spr)
 		// even if we aren't changing colormap or lightlevel, we still need to continue drawing down the sprite
 		if (!(list[i].flags & FF_NOSHADE) && (list[i].flags & FF_CUTSPRITES))
 		{
-			lightlevel = *list[i].lightlevel;
+			if (!(spr->mobj->frame & FF_FULLBRIGHT))
+				lightlevel = *list[i].lightlevel;
 			colormap = list[i].extra_colormap;
 		}
 
diff --git a/src/m_fixed.c b/src/m_fixed.c
index ce7471a2..01445738 100644
--- a/src/m_fixed.c
+++ b/src/m_fixed.c
@@ -33,7 +33,9 @@
 */
 fixed_t FixedMul(fixed_t a, fixed_t b)
 {
-	return (fixed_t)((((INT64)a * b) ) / FRACUNIT);
+	// Need to cast to unsigned before shifting to avoid undefined behaviour
+	// for negative integers
+	return (fixed_t)(((UINT64)((INT64)a * b)) >> FRACBITS);
 }
 
 #endif //__USE_C_FIXEDMUL__
diff --git a/src/p_floor.c b/src/p_floor.c
index 39748312..d143f6e9 100644
--- a/src/p_floor.c
+++ b/src/p_floor.c
@@ -2090,6 +2090,7 @@ void T_EachTimeThinker(levelspecthink_t *eachtime)
 	boolean floortouch = false;
 	fixed_t bottomheight, topheight;
 	msecnode_t *node;
+	ffloor_t *rover;
 
 	for (i = 0; i < MAXPLAYERS; i++)
 	{
@@ -2137,6 +2138,19 @@ void T_EachTimeThinker(levelspecthink_t *eachtime)
 			{
 				targetsec = &sectors[targetsecnum];
 
+				// Find the FOF corresponding to the control linedef
+				for (rover = targetsec->ffloors; rover; rover = rover->next)
+				{
+					if (rover->master == sec->lines[i])
+						break;
+				}
+
+				if (!rover) // This should be impossible, but don't complain if it is the case somehow
+					continue;
+
+				if (!(rover->flags & FF_EXISTS)) // If the FOF does not "exist", we pretend that nobody's there
+					continue;
+
 				for (j = 0; j < MAXPLAYERS; j++)
 				{
 					if (!playeringame[j])
diff --git a/src/p_setup.c b/src/p_setup.c
index 8f307df4..3deabb76 100644
--- a/src/p_setup.c
+++ b/src/p_setup.c
@@ -2561,11 +2561,6 @@ boolean P_SetupLevel(boolean skipprecip)
 
 
 	// Reset the palette
-#ifdef HWRENDER
-	if (rendermode == render_opengl)
-		HWR_SetPaletteColor(0);
-	else
-#endif
 	if (rendermode != render_none)
 		V_SetPaletteLump("PLAYPAL");
 
@@ -3115,7 +3110,7 @@ boolean P_AddWadFile(const char *wadfilename, char **firstmapname)
 
 	if ((numlumps = W_LoadWadFile(wadfilename)) == INT16_MAX)
 	{
-		CONS_Printf(M_GetText("Errors occured while loading %s; not added.\n"), wadfilename);
+		CONS_Printf(M_GetText("Errors occurred while loading %s; not added.\n"), wadfilename);
 		return false;
 	}
 	else wadnum = (UINT16)(numwadfiles-1);
diff --git a/src/p_spec.c b/src/p_spec.c
index 9aafc2ca..18314c2e 100644
--- a/src/p_spec.c
+++ b/src/p_spec.c
@@ -6722,6 +6722,7 @@ void T_Scroll(scroll_t *s)
 		line_t *line;
 		size_t i;
 		INT32 sect;
+		ffloor_t *rover;
 
 		case sc_side: // scroll wall texture
 			side = sides + s->affectee;
@@ -6763,6 +6764,19 @@ void T_Scroll(scroll_t *s)
 					sector_t *psec;
 					psec = sectors + sect;
 
+					// Find the FOF corresponding to the control linedef
+					for (rover = psec->ffloors; rover; rover = rover->next)
+					{
+						if (rover->master == sec->lines[i])
+							break;
+					}
+
+					if (!rover) // This should be impossible, but don't complain if it is the case somehow
+						continue;
+
+					if (!(rover->flags & FF_EXISTS)) // If the FOF does not "exist", we pretend that nobody's there
+						continue;
+
 					for (node = psec->touching_thinglist; node; node = node->m_thinglist_next)
 					{
 						thing = node->m_thing;
@@ -6826,6 +6840,19 @@ void T_Scroll(scroll_t *s)
 					sector_t *psec;
 					psec = sectors + sect;
 
+					// Find the FOF corresponding to the control linedef
+					for (rover = psec->ffloors; rover; rover = rover->next)
+					{
+						if (rover->master == sec->lines[i])
+							break;
+					}
+
+					if (!rover) // This should be impossible, but don't complain if it is the case somehow
+						continue;
+
+					if (!(rover->flags & FF_EXISTS)) // If the FOF does not "exist", we pretend that nobody's there
+						continue;
+
 					for (node = psec->touching_thinglist; node; node = node->m_thinglist_next)
 					{
 						thing = node->m_thing;
diff --git a/src/p_tick.c b/src/p_tick.c
index 1b1eea12..84c36835 100644
--- a/src/p_tick.c
+++ b/src/p_tick.c
@@ -608,7 +608,7 @@ void P_Ticker(boolean run)
 	}
 
 	// Keep track of how long they've been playing!
-	if (!demoplayback)
+	if (!demoplayback) // Don't increment if a demo is playing.
 		totalplaytime++;
 
 	if (!useNightsSS && G_IsSpecialStage(gamemap))
diff --git a/src/p_user.c b/src/p_user.c
index 8a9f2437..691ecee7 100644
--- a/src/p_user.c
+++ b/src/p_user.c
@@ -1747,6 +1747,9 @@ boolean P_InSpaceSector(mobj_t *mo) // Returns true if you are in space
 
 		for (rover = sector->ffloors; rover; rover = rover->next)
 		{
+			if (!(rover->flags & FF_EXISTS))
+				continue;
+
 			if (GETSECSPECIAL(rover->master->frontsector->special, 1) != SPACESPECIAL)
 				continue;
 #ifdef ESLOPE
@@ -1961,6 +1964,12 @@ static void P_CheckBouncySectors(player_t *player)
 
 			for (rover = node->m_sector->ffloors; rover; rover = rover->next)
 			{
+				if (!(rover->flags & FF_EXISTS))
+					continue; // FOFs should not be bouncy if they don't even "exist"
+
+				if (GETSECSPECIAL(rover->master->frontsector->special, 1) != 15)
+					continue; // this sector type is required for FOFs to be bouncy
+
 				topheight = P_GetFOFTopZ(player->mo, node->m_sector, rover, player->mo->x, player->mo->y, NULL);
 				bottomheight = P_GetFOFBottomZ(player->mo, node->m_sector, rover, player->mo->x, player->mo->y, NULL);
 
@@ -1974,7 +1983,6 @@ static void P_CheckBouncySectors(player_t *player)
 						&& oldz + player->mo->height > P_GetFOFBottomZ(player->mo, node->m_sector, rover, oldx, oldy, NULL))
 					top = false;
 
-				if (GETSECSPECIAL(rover->master->frontsector->special, 1) == 15)
 				{
 					fixed_t linedist;
 
diff --git a/src/sdl/i_video.c b/src/sdl/i_video.c
index df8af61b..0dd022a8 100644
--- a/src/sdl/i_video.c
+++ b/src/sdl/i_video.c
@@ -700,6 +700,14 @@ static void Impl_HandleMouseButtonEvent(SDL_MouseButtonEvent evt, Uint32 type)
 
 	SDL_memset(&event, 0, sizeof(event_t));
 
+	// Ignore the event if the mouse is not actually focused on the window.
+	// This can happen if you used the mouse to restore keyboard focus;
+	// this apparently makes a mouse button down event but not a mouse button up event,
+	// resulting in whatever key was pressed down getting "stuck" if we don't ignore it.
+	// -- Monster Iestyn (28/05/18)
+	if (SDL_GetMouseFocus() != window)
+		return;
+
 	/// \todo inputEvent.button.which
 	if (USE_MOUSEINPUT)
 	{
diff --git a/src/st_stuff.c b/src/st_stuff.c
index 7ddb50ef..0e0e9749 100644
--- a/src/st_stuff.c
+++ b/src/st_stuff.c
@@ -216,17 +216,17 @@ void ST_doPaletteStuff(void)
 	else
 		palette = 0;
 
+#ifdef HWRENDER
+	if (rendermode == render_opengl)
+		palette = 0; // No flashpals here in OpenGL
+#endif
+
 	palette = min(max(palette, 0), 13);
 
 	if (palette != st_palette)
 	{
 		st_palette = palette;
 
-#ifdef HWRENDER
-		if (rendermode == render_opengl)
-			HWR_SetPaletteColor(0);
-		else
-#endif
 		if (rendermode != render_none)
 		{
 			V_SetPaletteLump(GetPalette()); // Reset the palette