I can't reproduce the bug anymore...

How about displaying total number of beds next to number of beds in specific lair ?

You can see the bug when you load this savegame

Related to this bug

Related to this bug.

AI code is to blame. I got rid of all my beasts and workers started to collect gold.

Just slap your creatures onto lava.

There are no other tasks and vault is not full.

Other diggable tiles should be checked too.

You are right. They look fine when used to make water/lava fall.