There's a certain area around tags where they will flip constantly between their normal and hover states. Please see the following video for an illustration of the issue:
This is in Chrome stable in case it makes a difference.
Repro: Test here
Yeah, on Super User
border-bottom: 1px #6C0000 dotted; is more specific than the border defined for
.post-text .post-tag, and the variation in border definitions causes it to flip back and forth between the hover and non-hover states.
Tweaking the selector/adding the border definition to the
.post-text a.post-tag:hover style should fix things.