So I can write plenty of things, and hit ctrl-u to underline them, and they underline fine.
If I type…
D&D5e
then I press shift+home (to highlight the line), and press ctrl-u to underline, nothing appears to happen. If I add a space in the middle… so “D&D 5e”, the space is underlined.
Oddly, the little “U” in the formatting toolbar changes background color, so it thinks that text is underlined.
Add D&D5e to the user dictionary (right click, “Learn Spelling”), and the underline works correctly.
The misspelling indicator overrides underlining (which makes sense, sort of; the underline occupies the same space, and would obliterate the series of red dots).
I agree. I don’t care for it, and I think the spell check “dotted underline” should be about 2 pixels lower so it doesn’t occupy the same graphic space.