Flying critters spawn from eggs inside tiles

Has happened twice with shine bugs in this save, now with a puft. Always flying critters, always deep in a pool, always with a tile that forms a corner, being stuck in the tile despite being mostly positioned out of it, seemingly stuck via being just barely inside its edges (note that it was the right side with the shine bugs, so doesn't seem to be direction-dependent). They do not escape on their own and must be dug out. 

Scientific Spaceprison.sav