This is the weirdest flat I have ever heard of. After 12 miles into my ride last night I stopped at my parents house out in the country to check in with them & my grandmother. A little later one of my dads friends came to visit & while we were all talking outside I heard a noise that sounded like a .22 cal rifle going off. Guess what it was? My rear tire was flat when I went to ride back home, when I checked everything out the tube would hold 30lbs of air but would bleed the rest out. After trying to get it to hold air a couple of times I just replaced the tube with the extra I keep in my seat pack. I guess the valve stem just went goofy because if it got more than 30 lbs inflated it would just pull itself in & deflate. Has anyone else heard of this before?