One stem failed on my 5er for no apparent reason. Luckily Eileen was driving the 5er and I showed up about 20 minutes later with the M and its M Mobility system with which I was able to pump it back up long enough to get it to the nearest tire store and have it replaced. In 11 years of BMW ownership (multiple cars) this is the only failure for any reason. Sounds like incredibly bad luck on your part, but just in case there was a bad batch of rubber, have your local BMW service check the other two. It may save you from being stranded somewhere and they shouldn't charge you for checking.