Hi!

i found similar problem here http://away3d.com/forum/viewthread/2970/
Looks like we have the same problem on Away3d 4.1 Beta.

Details:
Entire scene is created in 3DMax (including planes) and imported using AWD2.
Trees are just planes with transparenct PNG as textures.
Now if u create any object and place it on scene behind trees and set its alpha<1 new object will be displayed on trees not behind them.
U can see this here:
http://www.test.taern.com/performanceTest/alphaBug.html

Radagast

This is no bug, this is actually a very general GPU issue.
Try play with zOffset, this should fix most if not all your issues.

Ok, thanks for reply, i will check this:)
[Edit]
I found great explanation of that problem here:
http://away3d.com/forum/viewthread/2623/

All is working fine now