Deseleting just one enumation literal with the Tool took me 5 minutes (!) and 15 seconds from click to reaction. The Tool occupied 50% of my dual core CPU within this time. As you can see in the pciture, the enumaration atribute (here: 'boundary' from 'referentType') is quite deep inside the tree, which is obviously the problem.
Jonas, can you assign this problem?
Will be included in release 2.2