Ok, the next version will fill the background with the back color if you specify VWMUseTransBlt but not VWMUseFakeTrans/VWMTransparent, even if you're using a backbmp. As I said, it might be a little bit before I can release it since there's some half-finished stuff right now.

Per-pixel alpha with png won't happen for a while, I have to figure out how much I actually have to change first, and it could be a lot.