I took your advice and checked out the par2-tab. I did see par-check activity (during download), but poorly did not see any unrar progress. Did I overlook something?
if the collection is gone from the par2-tab it has been cleaned up after unraring. if it's still there then something must have gone wrong.
as a hint when the tray-item turns purple unraring takes place if it turns yellow altbinz is repairing.
also if for some time u want to constantly monitor par-checking, repairing and unraring u can undock the par2-tab into a seperate always-in-front-window which u can then place anywher u like. simply drag the tab to the right until the hand becomes an arrow in front of an square... to undo it simply close the par2-window