When searching on any of the SO family sites, search terms are highlighted in the results with a background color. However, this tends to change result links' style to have no 'underlined' style on hover.
Was that intentional?
It's intentional by way of CSS working its styles in hierarchy.
Highlighted word in this case has a CSS style applied to it that comes ahead of the style that is applied to the line as a whole.
So in effect it kind of ignores what's going on in the background because the style that's applied to it takes the cake and the higher order of presentation value.