Unless the tendency is for air to flow inwards, which is how it works in our bathroom, and it seems in Jurek's.
Air flows outwards while you are running hot water, as it heats up and expands. Once you've finished your shower the hot saturated air starts to cool and cold air is dragged in (alongside air coming in from the door: it won't be a through draught).
I think you're greatly underestimating the draughtiness of my house...
