Using transparent images as tiles on tilemap lead to smearing effect

I'm building a randomly generated dungeon. My idea is to have an animated background behind the tilemap for which the non-walkable tiles (the tiles between the rooms) have to be transparent.

But I noticed that as soon as I use a transparent tiles for the tilemap, a weird smearing effect appears. But the effect does not appear everywhere. It only appears when you are close enough to the center of the sprite containing the tilemap.

Here is an example:


I already tried to mark the sprites with :markDirty() but that won't work. Is this a bug or am I missing something?