Didn't a MB MK 10 go off by itself in Cyprus after the pilot kissed, OK smacked, the runway rather hard?
I also seem to remember an F3 bounced off the sea and punched out the Nav (D### S####). I believe, seat was found with the handle still in place. Sadly the front seater was not so lucky.
It's a bit different to the seat going woof all on it's own I'll admit.