Like most things on the EX1 and EX3 apparently, this can loosen up over time. It's really easy to slide the metal tab off the shoe and tighten the little screws underneath. I've had to do this to both cameras. I don't know if it's because our cameras operate in ranges from -20 degrees F to over 100 degrees F, but I've had a LOT of screws loosen on the cameras. Not to mention the fact that many people thing *I* have a screw loose! :)
If you're going to hang something heavy on this shoe, it wouldn't hurt to actually remove those screws and apply some blue threadlocker or something. If the weight causes it to loosen while you're on a shoot, that could be inconvenient at best and risk breakage at worst.