>> >> With enlarged height and width, now the buttons are not vertically
>> >> aligned:
>> >
>> > Is this a screenshot of a tab bar or of a tab line?
>>
>> Tab bar.  And the change was caused by your commit db74a93659.
>
> Then I don't understand the two horizontally-adjacent images.  What
> are they? two separate frame?  If they are two frames, then where are
> the frame decorations?  In short, I don't understand what am I seeing
> there, and how did you get this display.

These are two separate images that show the changed tab dimensions
before changes when :margin was (2 . 0), and after changes
when now :margin is 4.

> And also, when you say "buttons are not vertically aligned", what
> exactly do you mean?  Not aligned with what?

Now buttons are not aligned to the baseline, and thus are
not centered vertically anymore.

>> db74a93659 that contains such changes:
>>
>> - :margin (2 . 0)
>> + :margin ,tab-bar-button-margin
>
> This is to make the code do what the variable's documentation says.
> Without that change, the images were sized using :margin '(2 . 0)',
> but the C code used the value of tab-bar-button-margin, a simple
> scalar, to place the image and clear its background.  The way to
> affect the image dimensions is by changing the value of
> tab-bar-button-margin, not by hard-coding the margin in the image
> properties.

This patch restores the original tab dimensions, while also keeps fixed
the reported problem of mouse face not clearing entirely: