I'm back :0
(VX Ace)
I created a custom tile for tileset D, which is basically a puddle. Around the puddle is the transparent colour, so it should show the floor around it in-game.
But when I painted the tile with the editor, behind my puddle displayed the very first sample tile from tileset A (a floor tile, as it appears when you select it with the wall showing at the top of the tile.) This is so random I can only assume it's a bug.
Does anyone know why this happened? My puddle is a similar shade of blue, but I don't think that's the cause...