Well that was a tough one. I was able to duplicate the error. The scenario goes like this.

Two artifacts art-1 and art-2

1. add a tag to art-1 called "artsTag"

2. save

3. add a tag to art-2 called (here's the kicker) "artsTag" Notice that the name is the same.

4. save - Hibernate error.

I'll save you from the gory technical details. We'll post a patch in the next couple of days.

The work around is to always either select a tag from the tag list or create a new one that is unique. The fault is on some code that tries to synch unique tag names with tags already in the database.