This post is for LaMorte. Look down at the front sprocket when it's happening. See if the pedals are cranking but the spocket isn't. I had this happen to a old peugeot I had. The inside of the front spocket was cut like gear teeth and it started jumping teeth. It's 1-piece crank. It probably has a keyed front spocket and it sheared off. Also keep a close eye on those fenders. I've read about several here that have had the vibration crack the fender mount then with no notice it suddenly try's to follow the wheel spin locking up the wheel.
Edit; I looked at the pic again your going to have to take the rightside chain guard off to see if that's what's wrong or have someone else watch from the side. It doesn't look like the front sprocket is pinned to the right pedal shaft (aka bmx style). This might be what's wrong. BTW, pretty bike, gratz.
