I just tried to spawn a big (around 60 blocks high) bo2 object on a mountain in my 256 blocks height world and the object got cut off at the height of 128. I guess it's a cap which is a relic of the times when world height was fixed to 128 blocks.

I'm sorry I did not answer the last month, but I was very busy with my studies, so I had no time for Minecraft.

I retried everything with clean files now and came to the conclusion that the problem I described in the first post only affects worlds with WorldHeightBits set to seven. Therefore I am not sure if this is a bug at all or if this can be considered "a feature" as maps with seven height bits are supposed to be only 128 blocks high.

My problem is, I have a world that was made when all maps were 128 blocks high and now I want to spawn bo2s that are bigger. Now I need to set "WorldHeightBits:8" but then new generated terrain will look very different?

Hmm can't repeat this.. may i see your bo2 object ?