So the bug could be fixed with that patch albeit not entirely
satisfactorily. I think I will install it with the help of a
customizable variable users would then have to set in their early init
files.
Assuming that this problem affects all or most users of recent GNOME, it would be fantastic to have this patch installed. It's a very unsatisfactory fix (because we don't understand what the problem really is, or even where, I think?), but the current situation is quite annoying (every time I open a new Emacs frame, I first have to resize it before I can use it).
Thanks again to Martin; having myself had to do quite a lot of proxy debugging of weird effects on systems I don't use, I appreciate the patience and hard thought that goes into trying to diagnose and fix this sort of bug.
--