So I did with the terraform mountain type 2 (small hill), which I wanted to cover with trees afterwards.
Now if I try to place one more layer on top, there is a crash.

I tried to reproduce with normal and debug version, the first debug crash gave 45MB logfile, so I did it again, and the output was more handy (~1MB).
Map and crashlogs here.
No need to tell me that too many blocks and too many trees are very hungry in terms of performance,
I know this, but there should not be any crash anyways
