bug#46827: Broken initial size of GTK3 frame

[martin rudalics]

>>> It seems tab-bar.el already updates only between 0 and 1.
>>
>> That's not what I've seen.
>
> There are no other values used in source code of tab-bar.el.
> But maybe sometimes the value of tab-bar-lines
> becomes more than 1?

It's 2 after the tab bar has been produced for the first time by the
display code.  And that is what's been causing trouble for you.  The
value was oscillating between 1 and 2.

>> But it's my experience that whatever we do to our frames, it's
>> hard to break the external menu bar.
>
> The bug was reproducible only on GNU/Linux, not on MS-Windows.

I've never been able to produce a "broken menu bar" on any build.

martin