> Sure thing:
Thanks. The geometry values are consistent with what you described.
This seems to be Bug#67654 and Bug#68463 and possibly Bug#65559. When
you run Emacs from a console or under gdb can you observe whether it
triggers a
gtk_distribute_natural_allocation: assertion 'extra_space >= 0' failed
Yes, both with Emacs 29 and git master produce this message when menu-bar-mode is non-nil, and the menu bar is drawn, in both window sizes (the normal sized window, and the strangely small one).
The one really notable difference to the above bugs is that the 29
version makes a shrunk frame only after you've removed the menubar while
master makes a shrunk frame immediately. Are the GTK versions of the
Emacs 29 build and the master build the same?
Yes, they are identical: gtk 3.24.41, Ubuntu build.
Just to make sure one thing: Would setting
'frame-resize-pixelwise' to t change anything?
So, I did (setq frame-resize-pixelwise t), then disabled menu-bar-mode (in Emacs 29), then C-x 5 2 (in both Emacs 29 & git master), and the new window was small, just as before. It seems therefore to make no difference.
Otherwise I would try to build Emacs with gtk2, lucid or motif.
I tried building Emacs git master with gtk2, and it doesn't fix the problem: the second window opened is slightly smaller than before (i.e. very small indeed).