To the original question - no, it's not acceptable and yes, they should all be fixed.
Speaking as one who always seems to be blessed with the person in front who crashes the seat back as soon as we're airborne, turns round to smile sweetly and ask if it's okay afterwards (knowing you can't really say no, it b.......y well isn't) then spends half the flight standing in the aisle anyway talking to his mates, so you've got an empty seat in your lap. And even has to be told by the cabin staff to put the darned thing to upright for a few brief minutes while you eat.
I'm going to get a paper round and start saving for upgrades. 