Have I missed something ?

[chihatchi]

Not really a problem, but a puzzle ! Needing to change the washer in a wash-hand basin tap, I turned off the whole water supply. As the tap I was to work on was still dribbling, I opened the bath taps which are lower, in order to drain it. Both, because the system is Combi boiler. No water came out of the bath taps, or any other open tap in the house except for the w.h.basin tap on which I was working, which continued to dribble for the whole time I was working on it; at least an hour ! How is this possible, when taps which are lower are open (and not dribbling) ? To me, it seems to deny a basic principle of physics. Doing the same job on the hot tap there was no dribbling. The only water anywhere in the system was that sitting in the cistern of the adjacent loo. It's possible that its level might be a couple of m.m. higher than the tap, but as its input by ball-cock is above the water level it wouldn’t be able to siphon out, and even if it did why would it go anywhere except to the lowest open tap ? The only tap higher than the w/h basin was in the kitchen, and that too was open. Is there any possible explanation for this ?