User blog comment:Supernova544/Weirdest discoveries ever/@comment-4583259-20121205075913

Hey yeah, that is pretty strange.

The game generates the terrain first, then it adds the plants, and then it decides if it's going to make an astro lair (or sometimes two). It carves out the tunnels, and it puts the polymer blocks only in cells that previously had some other material in them. That block you found in the tree is the one that gets generated at the top of the main vertical part of the astro lair. Usually you don't get that block at all, except sometimes when the astro lair entrance is completely underground. You can see one here: