Something funny my regulator did last weekend

[Elkman]

I got my Advanced Open Water certification at Wazee Lake last weekend.  (I also had a rather chilly night of camping, but that's another topic.)  I was using equipment rented from a local dive shop, since I don't have my own stuff yet.

I had a small problem with my regulator, though.  About 10 or 15 minutes into the night dive, I started hearing something freeflowing behind my head.  I wasn't sure what was going on, so I surfaced and tried to figure out what was going on.  My instructor and dive buddy came up after a bit, and I returned to shore to take a look at the problem.  It looked like the O-ring at the tank had blown out of position, or something like that.  I couldn't figure out if I did something wrong, like overtightening the tank valve, but I would have expected that to fail right away.  I continued the dive with another tank, and that worked okay.

The next morning, I did the deep dive, going down to 67 feet.  On the way back up, my instructor had me breathe from the tank hanging at 15 feet.  I thought it was a training thing, but when we got back to my surface, he told me that my first stage had been freeflowing again.  We got back onto shore and checked it out, and the O-ring looked like it had been cut just slightly.  We checked the regulator with a different tank and O-ring, and after yanking the valve around a bit, that O-ring blew out as well.  So, for the final dive, we swapped my hoses and gauges onto a spare regulator, and that worked just fine.

We checked the first stage and it looked like there may have been imperfections or some kind of small, sharp edges on the metal face where it mates to the O-ring.  I'm not sure how that happened -- I hope I wasn't tightening the regulator on too hard.  When I returned the equipment, the guy at the shop checked the regulator on the workbench and didn't have the same problem there.

Does this story sound like I was doing something wrong, or is it possible for a regulator to slash three O-rings in a row?  I'm at a loss to explain what happened.  At least I was able to finish my five dives needed for the Advanced Open Water certification, and I think my diving improved in the process -- I'm starting to get more experienced with buoyancy, which helps.