Sometimes Network Manager (and the network indicator) asks for passwords it already knows. This issue is intermittent and I'm not yet sure what causes it, but it has been happening for a long time on many different devices.
I'm seeing it happen in Ubuntu Touch on krillin (rtm 274, OTA3.5 candidate), but also on every other Ubuntu Touch device I've ever used and every notebook I've ever tried Network Manager on. This bug is specifically targeting Ubuntu Touch though.
The issue is easiest to trigger by rebooting the phone. While developing a new reboot loop test, I saw this happen on 8 of 12 boots during a short test sequence. The logs from that are attached, though I'm not sure if it contains nearly enough information.
Triggering the issue is sometimes difficult due to the intermittent nature, but in general it usually happens if I leave a device idle overnight. In the morning I'm greeted by a dialog asking for my wifi password. If I cancel the dialog it will connect successfully (though sometimes I also have to drag down the indicator and tap the network to tell it to connect), so it hasn't forgotten the password.
If more logs are needed, let me know which ones and I can add them to the test.
This looks like a duplicate of bug 615239. I've seen it in every Ubuntu release since Network Manager was introduced.