Edit: My last review was an error I made... I found out, that under specific circumstances the data either of Tree Stye Tab (-> TST) or Simple Tab Groups (-> STG) can become corrupt, which makes them behave "strange". I assume it was STG, which caused the issue, because when deleting a few big, but useless groups they shown further strange effects, which vanished after deleting them completely.
Forget my 3-Star-Rating, and my apologies!