I have opened inSSIDer 2.0 and found a bunch of networks
For each network i see the MAC address, SSID, RSSI, channel and other info.

I assume that RSSI is the strength of the signal.
I have two networks who both have -66 in RSSI
The line next to it is flat as no changes in RSSI is occuring.
However only one of the networks is still visible when looking at the graph.

Why is the RSSI still showing as -66 when my wireless card does not have any contact with it anymore?
In my logic the SSID should be marked as red or something to indicate lost connection.