Cisco Wireless :: WLC 5508 Radius Accounting

I have a WLAN configured with 802.1x PEAP pointing to an external RADIUS server.  It works fine for the most part, but I'm having problem closing accounting sessions in RADIUS.  I've found this is related to the client table in the WLC.  The user session does not end in RADIUS unless the WLC officially removes the client from the db, which takes 5-6 minutes from what I can see (probably due to the default idle timeout of 300 seconds). 
 
For example:
 
1.  I connect my tablet to the test WLAN.  It associates and authenticates successfully and the WLC sends the accounting info to my RADIUS server, opening up a user session.  If I turn off the wifi in the tablet, the client entry stays in the WLC client table until it times out.  The WLC removes my tablet from the client table after 5-6 minutes, and then the session closes in the accounting table.  I can force the session to close much earlier by manually removing the client from the WLC.
 
2.  Same as #1, but this time instead of turning of the wifi in the tablet, I choose to connect to a different WLAN in the WLC.  The user session in the accounting DB never closes.  If I reconnect back to the original test WLAN with 802.1x, it opens up yet another user session in RADIUS accounting.  Now I have a "dead" user session in accounting that is going to be open forever unless I delete it from SQL.
 
Is this an issue with the end user client not sending the disassociation frame properly, or a config problem with the WLC?  How can I make it so that every time a client drops from an AP or moves to a different WLAN, the WLC would immediately send accounting updates to my RADIUS server and close the user session properly?