>> But thhis last ConfigureNotify event is not explicable to me, values
 >> like 789x845 are unprecedented so far.  Does your WM deliberately
 >> resize the frame?
 >
 > Yes, pretty much like Emacs splits windows into two balanced halves.  I
 > have a 1600 pixel wide screen, 3 pixels gap between WM windows, and 3
 > pixel window borders.  That makes 1579 pixels width for actual WM
 > windows, divided by two (I've had a terminal at the left and emacs at
 > the right), makes 789.5 pixels per window.

Elementary.  But why should it react so allergically to our resize
request?  Basically, we have no choice: For some "normal" WMs we have to
tell them the size we want when the frame is mapped because before that
they may ignore our resize requests and after that the frame has already
appeared with its wrong size.  For a tiling WM requesting a size when
the frame is mapped is apparently a mortal sin.

Whatever it be, I attach a patch to address this issue.  It basically
means that on a tiling WM you cannot start with an iconic frame (but
doing so should not make sense anyway).  If people still want to do
that, we probably need a customizable variable where users tell Emacs
what kind of WM they use.

martin