On Mon, 2022-05-23 at 13:31 +0800, Po Lu wrote:
> It was fixed in December.  I installed a similar change along with
> some
> other fixes to child frames on PGTK, please test.

Thanks! Almost works.
I believe that the default value of child-frame-border-width should be
nil (that's the case for xfns and others), with this everything works
as expected for me.