The Real Issue of N900 is that it can't gather the new access points of the same WLAN.

Here what i meant, in the mall, you probably found a lot of access points of their WLAN network around (on the roof, wall, table). The point is when you walk away from the current access point, your N900 will not usually be able to use Internet anymore. You must wait or reconnect the network again in order for making it works.

:S