problem with billboard bushes

Hi,

I made some trees and bushes with tree creator. The trees look OK both up close and billboarded at a distance, but the bushes become boxy when they are at a distance. In other words, the round bush looks like a square box with a flat top when it is bilboarded at a distance, then pops back into the round as you get closer. Is there anything I can do to fix this? Thanks.

Zaffer

I have some tree creator trees and billboard has cut (flat) top. It looks like bug in shader.

Bump. This bug is only with tree creator trees. Imported trees are OK.