Pbs with Backing Store

Hello,

I have some problems with XRender (and Xft) with a window with
backing_store = Always or WhenMapped. If I draw with XRender/Xft on an
obscured region of the window it seems that XRender does not draw at
all (as it seems to me that XRender can draw as the content of the
window is stored by the server, e.g., I can XCopyArea the obscured
region). Of course when the obscured region become visible I've no
Expose event and at the end nothing is drawn.

Is this behavior intrinsic to the XRender protocol or I am doing
something wrong?
 
Thanks, Olivier