Previously there was a feature requested to add a title= tooltip to internal comment links. This was recently marked as
status-completed but was really only half implemented, as discussed in that post (how does one re-open an issue, anyway?).
Aside from the incomplete feature, there's a bug:
If a comment contains two or more links (ie. this post's first comment), then the tooltip for every link in the same comment has the same tooltip text, specifically the text from the first link.