Not sure if this is the right place to submit bugs, but couldn't find anywhere else suitable. Please let me know if there is another official channel to submit bugs.
When loading ArcGIS Explorer 1200 in a disconnected environment I noticed that it was constantly trying to connect and stream the basemap. It should really be able to see its disconnected and not try to get the basemap at all. Anyway, this was taking up cpu, so I decided to try and remove the basemap by going to Home>Basemap>Clear Basemap. This seems to hang ArcGIS Explorer indefinitely.
It seems if you open AGX first while connected, and then disconnect it knows its disconnected and can deal with it better. The constant streaming does not occur and neither does the hanging when removing the basemap.