Blank screencaptures when using multi monitors

[simbr]

If I have two monitors enabled (ATi Radeon Mobility 9700 on XP) then more often than not any caps I take from AVI files come out blank. I upgraded from my old free copy to pro lite to try and resolve this and it seemed to work initially but the problem keeps recurring.
The problem only exists when using the internal renderer, but if I select any other renderer then the OSD text is aso included in the screencap, but I don't want to turn the OSD off if I don't have to.
I can use the grab feature of ffdshow, but it is fiddly and I prefer being able to just press a button. The ability to easily make screencaps is the reason I first started using bsplayer years ago.