MapEd: special rotation rules for trees?

[RootlessAgrarian]

I've been experimenting with rotation and translation of objects and I find a curious thing: I don't seem to be able to rotate trees in any other axis than Y.

Leaning trees are pretty normal IRL, so I expected to be able to "tilt" them freely. But when I tried to rotate tree models in axes other than Y, the model just "shimmered" at me. Its local axes moved, but the visible model did not. Is this just how it is (trees will only rotate on Y axis) or am I doing something wrong?