I had a similar thing happen to me on a LHR-ORD Virgin Flight a couple of months ago.
Whilst boarding and sitting down, I noticed that the seat back wouldn't stay upright, so I informed an FA.
Imagine my horror when the captain came on the PA to say that a small fault had been found in the aircraft and Take off would be delayed for approx 20 mins while an engineer fixed it! I felt bloody awful and wished I hadn't even mentioned it.
Anyway, the engineer quickly fixed the seat and we actually departed pretty much on time. During rotation on take off, yes you've guessed it, the seat flew back. Now economy seats may only recline 6 inches, but when the aircraft is climbing, that extra angle that the six inches gives you seems pretty bad! An FA could see me struggling to lean forward a bit but couldn't move obviously and I was essentially pinned back into the seat!
Once in the cruise, I was told that I would have to be located to another seat and this is where I got my hopes up as the cattle class was supposed to be full.
I had visions of my cruising in comfort for a change with all the other business class passengers, but unfortunately they managed to find me a seat in the middle row near the back of a jumbo.
Damn, I had lost my cushy window seat in exit row to be place in the middle of a group of hyperactive and noisy teenagers.
Ah well, such is life.
Anyway, back to the point (if I ever had one), I have to say that my experience couldn't have been more different than yours
chrisN as all the crew on board were professional and courteous when I presented the problem to them. Had they behaved like the ones on your flight, then I would have thought twice about flying that airline again.