When you bulk edit and change the label, the entire label set gets replaced. it would be nice if there were a way to add/remove labels instead of replacing them. Some people probably do this bulk change thinking they are adding a new label but end up removing the existing labels.
Certainly not a critical enhancement but one I though of because we had the same issue with ClearQuest keywords. Bulk editing (add/remove/replace) label sets would be a nice feature to have.