In languages or viewports that make some navigation links span across multiple lines, surprisingly only parts of the hovered anchor text get underlined:

The underline only decorating some of the lines makes it a bit puzzling for a moment, not being clear what words are actually part of what link etc.

This also happens in main menu when the items don't fit on one line:

The underlines were coded this way to match the visual design assets provided, instead of the implicit style the typeface provides (or, doesn't) by itself.
(Not to be confused with #15683, that has the decoration animated, and has extra markup.)