As stated above, mine came off too. The BB spindle is splined all the way, so if the crank arm is on, the splines are engaged. However, it doesnt take much movement (outwards) before itll make a faint "click" with each revolution of the crank as it begins sliding off the spindle and moves each revolution under pedal pressure. If you hear this, stop and get it properly installed and torqued.
I dont know if the shop reinstalled the small shim/spacer on mine, or not...I'll have to look and see.
Regardless, I've checked the torque on mine before every ride recently, and after a couple of slight movements on the torque wrench initially, the most recent rides the bolts were still fully tight - no movement in the torque wrench.
I'm of the opinion that the bolts weren't properly torqued at OEM installation, and that the shim/spacer may or may not be needed.