David De La Harpe Golden wrote:

> (i) N.B. Extension happens anyway, if the background happens to be
> different to the frame background 

Anyway, if you do consider it a bug that that extension happens, then
just making underline and overline drawing use width rather than
background_width (like overstrike) in src/xterm.c probably resolves
that? (at least on bitmapped displays)

Illustrative screenshots included - note how a nonmatching background
causes the ugly (in this context) extension.