diff --git a/specs/udmf_zdoom.txt b/specs/udmf_zdoom.txt
index 0fe7b1e8e..112e54bfc 100644
--- a/specs/udmf_zdoom.txt
+++ b/specs/udmf_zdoom.txt
@@ -224,13 +224,11 @@ Note: All <bool> fields default to false unless mentioned otherwise.
 	                                  // 0 meaning that the default is to be used, 2 equalling the density of a light level of 250, and 255 equalling the density of
 	                                  // a light level of 0.
 
-      portal_ceil_alpha = <float>     // translucency of ceiling portal (default is 0 (not visible))
       portal_ceil_blocksound = <bool> // ceiling portal blocks sound.
       portal_ceil_disabled = <bool>   // ceiling portal disabled.
       portal_ceil_nopass = <bool>     // ceiling portal blocks movement if true.
       portal_ceil_norender = <bool>   // ceiling portal not rendered.
       portal_ceil_overlaytype = <string> // defines translucency style, can either be "translucent" or "additive". Default is "translucent".
-      portal_floor_alpha = <float>     // translucency of floor portal (default is 0 (not visible))
       portal_floor_blocksound = <bool> // floor portal blocks sound.
       portal_floor_disabled = <bool>   // floor portal disabled.
       portal_floor_nopass = <bool>     // ceiling portal blocks movement if true.
diff --git a/src/gl/scene/gl_portal.cpp b/src/gl/scene/gl_portal.cpp
index 02fd9b452..86ea68b39 100644
--- a/src/gl/scene/gl_portal.cpp
+++ b/src/gl/scene/gl_portal.cpp
@@ -777,6 +777,8 @@ void GLPlaneMirrorPortal::DrawContents()
 		ClearScreen();
 		return;
 	}
+	// A plane mirror needs to flip the portal exclusion logic because inside the mirror, up is down and down is up.
+	std::swap(instack[sector_t::floor], instack[sector_t::ceiling]);
 
 	int old_pm=PlaneMirrorMode;
 
@@ -794,6 +796,7 @@ void GLPlaneMirrorPortal::DrawContents()
 	gl_RenderState.SetClipHeight(0.f, 0.f);
 	PlaneMirrorFlag--;
 	PlaneMirrorMode=old_pm;
+	std::swap(instack[sector_t::floor], instack[sector_t::ceiling]);
 }
 
 void GLPlaneMirrorPortal::PushState()
diff --git a/src/gl/scene/gl_sprite.cpp b/src/gl/scene/gl_sprite.cpp
index f79549a39..642e31c91 100644
--- a/src/gl/scene/gl_sprite.cpp
+++ b/src/gl/scene/gl_sprite.cpp
@@ -916,7 +916,7 @@ void GLSprite::Process(AActor* thing, sector_t * sector, int thruportal)
 				RenderStyle = LegacyRenderStyles[STYLE_Translucent];
 				OverrideShader = gl_fuzztype + 4;
 				trans = 0.99f;	// trans may not be 1 here
-				hw_styleflags |= STYLEHW_NoAlphaTest;
+				hw_styleflags = STYLEHW_NoAlphaTest;
 			}
 			else
 			{
diff --git a/src/gl/textures/gl_material.cpp b/src/gl/textures/gl_material.cpp
index dd224b8e0..5aa1d75b9 100644
--- a/src/gl/textures/gl_material.cpp
+++ b/src/gl/textures/gl_material.cpp
@@ -187,6 +187,7 @@ unsigned char * FGLTexture::CreateTexBuffer(int translation, int & w, int & h, F
 {
 	unsigned char * buffer;
 	int W, H;
+	int isTransparent = -1;
 
 
 	// Textures that are already scaled in the texture lump will not get replaced
@@ -224,14 +225,16 @@ unsigned char * FGLTexture::CreateTexBuffer(int translation, int & w, int & h, F
 			int trans = tex->CopyTrueColorPixels(&imgCreate, exx, exx);
 			bmp.CopyPixelDataRGB(0, 0, imgCreate.GetPixels(), W, H, 4, W * 4, 0, CF_BGRA);
 			tex->CheckTrans(buffer, W*H, trans);
-			bIsTransparent = tex->gl_info.mIsTransparent;
+			isTransparent = tex->gl_info.mIsTransparent;
+			if (bIsTransparent == -1) bIsTransparent = isTransparent;
 		}
 	}
 	else if (translation<=0)
 	{
 		int trans = tex->CopyTrueColorPixels(&bmp, exx, exx);
 		tex->CheckTrans(buffer, W*H, trans);
-		bIsTransparent = tex->gl_info.mIsTransparent;
+		isTransparent = tex->gl_info.mIsTransparent;
+		if (bIsTransparent == -1) bIsTransparent = isTransparent;
 	}
 	else
 	{
@@ -239,7 +242,8 @@ unsigned char * FGLTexture::CreateTexBuffer(int translation, int & w, int & h, F
 		// Since FTexture's method is doing exactly that by calling GetPixels let's use that here
 		// to do all the dirty work for us. ;)
 		tex->FTexture::CopyTrueColorPixels(&bmp, exx, exx);
-		bIsTransparent = 0;
+		isTransparent = 0;
+		// This is not conclusive for setting the texture's transparency info.
 	}
 
 	// if we just want the texture for some checks there's no need for upsampling.
@@ -247,7 +251,7 @@ unsigned char * FGLTexture::CreateTexBuffer(int translation, int & w, int & h, F
 
 	// [BB] The hqnx upsampling (not the scaleN one) destroys partial transparency, don't upsamle textures using it.
 	// [BB] Potentially upsample the buffer.
-	return gl_CreateUpsampledTextureBuffer ( tex, buffer, W, H, w, h, !!bIsTransparent);
+	return gl_CreateUpsampledTextureBuffer ( tex, buffer, W, H, w, h, !!isTransparent);
 }
 
 
diff --git a/src/namedef.h b/src/namedef.h
index bb9d27f40..d50f8131d 100644
--- a/src/namedef.h
+++ b/src/namedef.h
@@ -518,14 +518,12 @@ xx(Alphaceiling)
 xx(Renderstylefloor)
 xx(Renderstyleceiling)
 xx(Waterzone)
-xx(portal_ceil_alpha)
 xx(portal_ceil_blocksound)
 xx(portal_ceil_disabled)
 xx(portal_ceil_nopass)
 xx(portal_ceil_norender)
 xx(portal_ceil_overlaytype)
 xx(portal_ceil_useglobaltex)
-xx(portal_floor_alpha)
 xx(portal_floor_blocksound)
 xx(portal_floor_disabled)
 xx(portal_floor_nopass)
diff --git a/src/p_udmf.cpp b/src/p_udmf.cpp
index b0427045c..461feb9c8 100644
--- a/src/p_udmf.cpp
+++ b/src/p_udmf.cpp
@@ -1582,10 +1582,6 @@ public:
 					tagstring = CheckString(key);
 					break;
 
-				case NAME_portal_ceil_alpha:
-					sec->planes[sector_t::ceiling].alpha = CheckFloat(key);
-					break;
-
 				case NAME_portal_ceil_blocksound:
 					Flag(sec->planes[sector_t::ceiling].Flags, PLANEF_BLOCKSOUND, key);
 					break;
@@ -1607,10 +1603,6 @@ public:
 					else if (!stricmp(CheckString(key), "additive")) sec->planes[sector_t::ceiling].Flags |= PLANEF_ADDITIVE;
 					break;
 				
-				case NAME_portal_floor_alpha:
-					sec->planes[sector_t::floor].alpha = CheckFloat(key);
-					break;
-
 				case NAME_portal_floor_blocksound:
 					Flag(sec->planes[sector_t::floor].Flags, PLANEF_BLOCKSOUND, key);
 					break;