Well, I guess I brought myself bad luck by commenting on this subject; I just got a roll of slide film back, taken with a 1930s Wirgin folder, and there are noticeable light leaks at the edge of some frames from the red windows!
I've used this same camera a zillion times in much brighter conditions without a problem, so I suspect I loaded it just a little off alignment or something like that. (The light looks like it bled around the edge of the backing paper rather than "burning" through it.) I need to eat my words about *never* having had a problem, though.
That could just as easily have been from the roll not winding tight enough on the takeup reel. Many cameras have a spring that drags the back of the takeup roll to alleviate this problem.