Thank you for reporting this bug.
Do you have anymore context to help us find this bug? Does it happens often? Do you know the version of your OS 9Mac OS 10.7 or 10.8)?
I've seen this a few times when syncing just keeps on spinning. Mac OS is 10.8.3
Hi Bruno, just happened again. The syncing wheel has disappeared. Cannot close the app unless i go in menu close Producteev