Thanks for the update.
Here's what I think possibly happened:
If the device was added via auto-discovery, then it takes on the characteristics of the Device Setup -> Communication -> (select device type). The Device Setup entry does not overwrite existing entries. Now if the controllers were added manually, then you would have inputted the community string at the time of adding (or it defaults to 'public' in most cases).
On a sidenote, please try again to do the SNMP walk since that functionality should be working.