Just discovered that my N900 is trying to connect to an unknows wireless network because it was connected to one that uses the same name (SSID) eariler.
So if you connect to a wireless network called Linksys, it'll always connect to any network that has the same SSID, instead of verifying the MAC Address.

Can someone confirm this?
https://bugs.maemo.org/show_bug.cgi?id=6315