On the 6600? If you thread the take up lever the opposite way (left to right instead of right to left) the thread shouldn't come out.
I'm trying to understand this...so it makes a loop around the take up lever? (and you see the thread crossing itself underneath?)
Yesterday I had the thread-coming-out-of-the-take-up-lever a few times ... but of course I didn't realize it until I'd had a bunch of nasty retries (operator error).