When editing a question, hovering over the question's tags does not pop up the tag bubble.
As edits can involve re-tagging, being able to see the excerpt in the tag bubble would be really useful as a reminder of the exact tag usage.
It would make it easier to accurately determine if the tag is viable for that particular question or not.
(I cannot remember them all, although maybe that's just because I'm getting old..).
I'm going to assume this is not by-design as I cannot think of a reason for not having this functionality.
And I'm going with "bug" not "feature-request" because I am guessing this should already happen.