Hi 3am, thanks for your reply!
In fact, i've changed every frame image yet, aero & basic, all subsections (normal, fading, toolwindow, aero peek & shadowless in Aero, each "caption" image in Basic).
They're now all totally white square images with transparency at 30% for active & 10% for inactive...
But maybe i forgot something somewhere... Are they all in "Windows & Caption Buttons"...?
Thanks for your help!!!