Outlook/Exchange Sync Issues - Problems in cached exchange mode

I was helping troubleshoot a users in ability to send/receive messages within Outlook. We are running Microsoft Exchange 2010 and are using cached exchange mode within Outlook(somewhat troublesome but apparently necessary with extremely large deployments of exchange). The user deleted their entire mailbox except for about 15MB worth of mail, though they were still seeing in OWA (Outlook Web Access) that their mailbox was over the limit by about 500MB. Reviewing the folder properties in Outlook showed a discrepancy between the local cached copy and the server copy of about 500MB in the Outbox folder. Nothing that we were doing was proving successful. We tried creating a new local profile within Outlook, tried performing various tasks in OWA, nothing was working. We could not get the Outbox folder to update. Our next thought was to try and see what was in his Outbox on the server. OWA only shows the core mail folders (Inbox, Sent Items, Deleted Items, etc.) but we needed to see the Outbox. I did not want to toy around with Powershell so I turned to google... The solution ended up being to sign into OWA in using the light version, which allows you to see all folders within your mailbox (makes no sense, right?). We were able to view the Outbox folder and purge the offending mail clearing up the issue. The next step is to determine how his Outbox ended up so full of old messages that it accumulated enough to fill up his mailbox. We are currently monitoring the users cached and server copies to see if a discrepancy occurs. If I find out what caused this, I will surely post.