Bleed thing just more or less came off in my hand!?

Ok, so it's after midnight and I think to myself...why not bleed the bathroom radiator? So I bleed it successfully but then I start to tighten it and without warning the whole thing goes really loose and wobbly...by that I mean the square rod and the circular thing that loos like a nut are just wiggling about in the hole. First I thought the whole system was just going to drain out onto the floor, but nothing happened, so I then thought I'd turn on the boiler and see if that made it leak. Still nothing. Do I need to worry about this? I live in a rented flat and the landlord is pretty useless about fixing things.

By the way, the radiators are quite old but the boiler is 2 years old and is a Worcester 28i junior. The pressure is very low because of persistant slow leaks from all the inlet valves since the new boiler was put in.