Overline / underline setting in mode-line and mode-line-inactive fonts creates visual artifacts

[rommeswi]

By default, Emacs 29 sets mode-line and mode-line-inactive fonts to have overlines and underlines.
Powerline inherits these fonts and this can create rather ugly effects. In particular, any spaceline theme looks completely broken. While this may just be a spaceline issue, it would be perhaps more natural for powerline not to inherit the underline properties of mode-line and mode-line-inactive. If a theme needs underlining, it could purposely set the underline property for its font.

Here is an example using spaceline: