Eli Zaretskii <eliz@gnu.org> writes:

> This would take care of the conflicting colors, but that's not the
> original problem which caused us to talk about tooltips.  The original
> problem was that someone could customize the help-key-binding face to
> specify size as well.  What do you see then?

It works as expected also when you specify :height.

>> +          (add-face-text-property 0 (length text) 'tooltip t text)
>
> This should have a comment explaining why we use a non-nil APPEND
> argument.

Fixed in the attached.