Comment 1 for bug 1390205

system-image (dbus or cli) just sets the flag in udm, and let's udm handle all the details. One thing that would be interesting is to know whether leaving and returning to your wifi, with wifi-only downloads enabled, crashes udm or not. If udm crashes without sending any further signals to s-i, then s-i-dbus will just continue to spin until its own internal timeout triggers (defaulting to 10m). After 10m with no response from udm, the reactor will timeout, cause a s-i-dbus error and that process should exit. s-i-cli should, after 10 minutes of no response from udm, also timeout its reactor, and exit with an exception on the console (and log file).

If this is reproducible, then tailing /var/log/system-image/client.log, the udm log file (don't remember where the system bus udm log file lives), and ps'ing 'ubuntu-download-manager' to see if it crashes would all be useful things.

Ultimately you're right by filing the bug here. s-i does not currently do any direct querying of the network status.