I made a mistake. Fuck git reverts, they are a nightmare, let's just do this the old fashioned way.

src/p_slopes.c

@@ -546,17 +546,9 @@ static pslope_t *P_NewVertexSlope(INT16 tag1, INT16 tag2, INT16 tag3, UINT8 flag
 			continue;
 
 		if (!ret->vertices[0] && mt->angle == tag1)
-		{
 			ret->vertices[0] = mt;
-			mt = mapthings;
-			i = 0;
-		}
 		else if (!ret->vertices[1] && mt->angle == tag2)
-		{
 			ret->vertices[1] = mt;
-			mt = mapthings;
-			i = 0;
-		}
 		else if (!ret->vertices[2] && mt->angle == tag3)
 			ret->vertices[2] = mt;
 	}