I'm having problems with cancelling an ongoing large sync.

Because my computer slows down too much if I'm simultaneously doing my current large initial sync and photoshop editing, I'm currently running the sync manually, and cancelling it when I want to work, and then starting it again when I stop.

But when I click 'Cancel', and it changes to 'Cancelling...' it continues syncing for some time. I tried simply quitting via the menu item, but that seems to have corrupted some of the files in the source folder (unless that's just a coincidence that it was the files that were being encoded at the time that ended up corrupted - I guess it could be that they were already corrupt and the program was stuck trying to encode them...?.