X11 backing store

[Hans Werner Strube]

If X11 graphics programs request backing store, for instance, with
    drawattr.backing_store = Always;
    XChangeWindowAttributes(display, drawable, CWBackingStore, &drawattr);
this seems to have no effect. The same program works correctly in Solaris
(SPARC) and IRIX (MIPS).
The memory of my graphics card (8 MB, Rage Mobility) appears sufficient,
since the whole screen would only use 2.3 MB with 24 bits/pixel. It would
be desirable to have this possibility to avoid explicit redrawing after
a portion of the window has been covered or the window has been iconized
and reopened.