The Swedes had a accidental ejection (in flight) on a JAS39 back in 2007. Is that the same type of Mk10 MB seat? In that case the pins where (naturally) not installed, but they did have incidents on ground on different aircraft with the ejection handle moving out of place when removing pins. Including when collecting a brand new one at the factory I believe.
The inflight one was caused by the anti G suit moving the handle. (Pilot got ejected when pulling G on break over the airfield) Any relevance to this case, or different design?