I had a similar situation happen to me. I parked and launched but didn't notice my Icom missing until was well past the surf. I assumed it fell off because I wasn't sure if I had clipped in the strap. Now you have me wondering if someone walked off with it. I'll be thinking twice about what I leave in plain sight. I've been taking for granted my theft free record in the past.
BTW: I lost mine a long time ago and have since replaced it.