In 0022607, I described the problem of having dozens of unused tags in the database. In Mantis 2.28.0, the "unused" tag filter was introduced to help cleaning up unused, tags, however the execution is unfortunately flawed, not really making the process any less tedious than it was before:

1. Apply the unused tag filter.
2. Click "Delete" on a tag.
3. You are redirected to to a confirmation page. Effectively this means that you have to move the mouse pointer to a completely different place on the screen, which is tedious.
4. Once you confirm the deletion, you are returned to the tag overview, however the unused filter is no longer applied. This means that you have to move the mouse again to the unused filter, and then proceed with deleting the next tag.

As you can see, the actions needed to delete all unused tags are still very tedious. As a first remedy, the last used filter should probably remain active after confirming a deletion. However, even with that in place, having to move the mouse constantly between the first tag ain the list and the confirmation button for actually deleting the tag would still be very tedious. As it makes sense to keep the confirmation dialog, I think a dedicated "delete all" button would still be the only user-friendly option.