> Yes. We resize the GtkFixed where the text-part and scrollbar resides in Emacs. The layout widgets can not handle the layout of Emacs (i.e. text with scrollbar, modeline without scrollbar, minibuffer with scrollbar). If the scrollbar is 16 pixels wide no matter what, and Emacs thinks it. is 12, the sizing will be wrong.

I see.  But here I have to explicitly set the scroll-bar-width frame
parameter to make sure that no extra space is drawn.  Maybe we should
document this somewhere.

 > You have to add 2 x trough-border, i.e 2 x 1.

Aha.  So is it the trough-border that doesn't get always cleared
correctly when deleting/resizing windows or is it some extra space
between trough-border and the surrounding objects?

I attach a screenshot where you can see the effect with the scrollbar in
the upper window.

martin