Comment # 5 on bug 908258 from Michal Srb

(In reply to Stefan Dirsch from comment #4)
> Dejavu? Michal, didn't we see this issue already with one of the icewm
> themes?

We did, it was bnc#856931. The problem is that if the XPM has transparent color
(even if it is not used), libgdk creates mask for it. The mask is created by
drawing horizontal lines. That is terribly ineffective and X server wasn't
rendering corner cases consistently (lines going from point A to point A, i.e.
having zero length, were sometimes rendered as one pixel, sometimes not at
all).

At that time I didn't get proper answer from upstream about how should X server
render it, fix for gdk would require quite big rewrite, so we just workarounded
it by removing the unused transparent color from the problematic XPMs in icewm.

If there is fix now in X server, let's backport it.