Could possibly be the battery on its way out, as you said it was stood for a week. I know you said voltage looks normal but maybe pop a battery charger on and see how much charge you've got.
When my battery was in its final throws, the headlights were coming on with the lights switched off, and i couldnt get them to switch off at all until i disconnected the battery! I dont know what causes that, i'm guessing some sort of odd voltage issue makes it spaz out.