Yes, it is possible. I have seen it happen before, when the lines start to wear out or rust near the joints, air gets in there, and then when you press on the pedal, it moves the line slightly and seals it. This is highly uncommon, and I have only seen it happen once, and we did notice it by the wet area around the threads. I have also heard of it happening with the copper washer, but this is usually on installation and it's highly irregular.
I'd bleed them yourself by gravity, we just discussed how on this BBS, try a search as well. If you still want them to bleed them, just let them know and they'll do it, but be prepared to shell out some more $$$ if the master is toast.
JEEPN
Winter Harbor, Maine
'81 CJ-8 Scrambled, It's a Jeep, Chevy, IHC kinda thing!
'88.5 Zuki, 7" Lift, Locked, Swamped, Rolled, and just generally broken in right!