I've noticed this on a number of occasions, most of which are too trivial to mention, that Window 7 offers you a dialogue box asking you whether you want something done or not, you click what you want, but it then goes and does the opposite.
Most recently Windows wanted to restart to finish intalling updates. It offered me the possibility of restarting later, which I clicked because I was midway through some heavy downloads. Within a minute it just went and restarted anyway against my instructions, scuppering the downloads.
I often get the sense with Windows 7 that I am not the owner of my computer. In fact it doesn't seem to have regard that you might actually be using the computer for something more important than its own petty machinations.