FT QL Mirror Behaviour Question

I've acquired an FT QL (original FT, not FTb), and the mirror stays up until I operate the film advance, when it drops down. I expect its a fault as I know they normally have instant return mirrors, but I wondered if perhaps there was an early version without this feature?

 

If I operate the mirror lock up, it stays up all the time. Otherwise it flips up after trippung the shutter, then drops back down upon turning the film advance.

Even the Canonflex has an instant return mirror, so I doubt this was something that was omitted from early FTs.

 

I'd take a close look at the damper foam. I've seen it get so sticky that it will hold the mirror.

Thanks for this Ben. Thinking about it the FT came out in 1966, whilst the non-instant return mirror SLR'a were pretty much extinct by 1960. It's not sticking to the mirror foam, it must be the mechanism itself. The speeds slower than 1/15 don't work either.