I think it mostly has to do with how dry the air is around you where you go to smoke it. I've had verry few problems down here in South Florida and had big issues when on vacation up North.
It used to be common for people to stick their cigars in their mouth to get the wrappers wet before smoking. It was said to keep the wrappers together and I've tried it and it does work. Don't see people do this very often these days, but once in a while I catch someone.
Just dont do it with a 6 X 56 ring monster in a bar unless you are prepaired to have a guy offer to buy you a drink.
I have to agree with Mitch, here. I have more trouble in dryer climates and in colder climates. I can't say I've had one unravel entirely, but what I've been reading seems to describe what I would explain as a small split and unravel below the lit end. I would say that humidity change or even overly humidified sticks cause the problem more so than dry cigars- and the greater difference you have in the atmosphere in humidity, the worse it seems to be.
Try dry-boxing your cigars for just about an hour before you smoke, you may see a difference. When I have a split-unwrap happen while smoking, I lick my thumb and apply some moisture to underside of the the rising wrapper, then gently smooth it back down. Doesn't always work, it has helped.
Bear