With the exception of the Tornado Type 10A, all modern (gas) MB seats have an interlock between seat pan handle mechanism & the man sep (i.e. the former needs to be pulled begore the latter will operate). Dare say interlock was designed in precisely as a precaution against inadvertant in-ac operation.
Why no interlock on Tornado? The compromises of the tri-national project. Neither is there a main gun safety pin on Tornado - and just one seat state - 'safe' - rather than the 'safe for parking' & 'safe for maintenance' pin positions on most other MB seats.
There were two theories after Dunsfold. The one already discussed was motoring the seat down onto a rogue wander lamp. The other was that the seat could have been mis-rigged in the bay prior to installation resulting in the man sep interlock being ineffective. Post accident, there was another less publicised mod in the front of the seat that removed the possibility of mis-rigging.
Significantly for a Harrier pilot, the relative (L&R) positions of the EO & mansep handles are transposed between the Type 9 seat in Harrier GR3 and the Type 12 in the then GR5. Thus the other theory was did Mr Taylor - with all due respect to a wonderful TP - who was programmed to pull the EO, and who also flew Harrier 1s, had a cognitive failure and operated the incorrect handle - with the interlock that should have saved him not working.
As the seat remains unrecoverable in the aircraft at the bottom of the Atlantic, the official report came down on the side of the wander lamp theory rather than mis-rigging plus cognitive failure (balance of probability stuff). However, there has always been much debate.
Not too many years later, an F3 mate nearly came to the same fate as Mr Taylor. Went for a (contingency) planned pull of his EO on recovery to Conz and possibly had a L/R cognitive failure. Man sep handle operated (remember no interlock on Tornado) & drogue followed by parachute (shredding) fired through the canopy. Fortunately, a confirmed error was that he had inadvertently looped his knee pad strap through the man sep handle prior to tightening it to his leg. Effectively, he had strapped himself to the seat via his knee pad, and that alone kept him in the aircraft - albeit with his head poking half out of the shattered canopy. With literally fingertip control of throttles and stick & no comms to anyone, he flew the last 15 miles or so to Conz (local knowledge). Nav had quickly sussed what had happened (couldn't eject because pilot's para rigging lines were across his canopy) and although pilot lost control at touch down (remains of parachute blossomed & yanked him further out of seat) it was a trainer ac, so nav kept it on runway & brought it to a halt!! Pilot had a very sore knee for a quite a few days. A very lucky man - with the horrific cosequences of one mistake being nullified by the consequences of a separate bizarre error.
BK