if you open the valve up, its possible to fill the cylinder with water, through the valve.
first i knew was the flashing blue lights outside - my hag of a neighbour had only called the fire brigade - said i was "tipping gas down the drain" after seeing the water leaking out of the cut.
firebrigade were confused too, but told her that everything was in order.
she then called calor gas...
chap said that id kill myself. i told him that, given that id done it, and we were talking on the phone, i disagreed.
they still were not happy at all though, and threatened all sorts of nonsense.
I take it your neighbour isn't on your Christmas card list then
ps. you would be advised not to prompt me further - we could be here all day! ; )