This sounds suspiciously like
what happened with my K-x (minus the battery drain issue - but that could be a quirk of the K-5 in this situation). In my situation, it was actually user error in that I managed to get crud into the shutter gears. My K-x was out of warranty so I poked it (the gear) with a small flathead screwdriver and then blasted the offending spot with compressed air. If your camera is still under warranty I wouldn't advise using my fix, but my camera has been working perfectly since I took the air to it.
EDIT: I didn't take my camera apart, you can see the gear next to the mirror when you take the lens off the camera. It just took a small poke with the flathead to allow the camera to finish cycling the shutter. I'd average anywhere from a couple to a couple dozen shots between the shutter sticking (both open and closed) until I sprayed down the gear itself with the air.
EDIT II: FWIW, I've shot well over 1,000 shots since I took the air to the camera without any problems. Did you swap lenses at all shortly before you had your problem? In my case I'm thinking I had lint or something stuck to the bottom of the lens I swapped over to in the dark and managed to crud up my camera that way.