It's because you're writing to the z-buffer even with the transparent hair, right? You're using transparency in the opaque stage. The sky is actually rendered after the opaque stage, probably so that fewer sky pixels get drawn (although I personally think there should be a flag to enable the sky being rendered first [as it affects some of my own effects], I've never raised this in the "Future" forum).

That's what I think is the most-likely cause, anyway. Render her (or just her hair if they're separate) in the translucent stage (there's a flag for that, but I can't remember what). The problem here will be potential sorting errors with other transparent objects.

Actually I'm just guessing that A7 renders the sky after the opaque stage, but it makes sense to me, and I know a lot of other rendering engines do it in that order.

Jibb