Originally Posted by MothrNatr

May seem to be a silly idea, but if you are cutting flannel and using a new blade, could there be a build up of lint in your cutter? This may cause the nut not to tighten correctly. Try cleaning your rotary cutter and make sure that your screw/nut is tight.

edited - only read to page three before I responded. Who knew that the answer was on page 5?? Oh well, my advice is still good. Glad you found the culprit!