Outlook 2007 - outlook.pst file displaying larger than 8 GB

I have a PC running XP Pro SP3 and Office 2007 Pro SP3. All Microsoft updates are up to date.
The user is running Outlook 2007 with an internet email account (not Exchange Server)

The user called me and stated she was checking her email in the “Inbox” from her PC and all of a sudden all of the Inbox contents were gone. The inbox was completely empty. When she clicked “Send and Receive” she would receive new email. She also had no issues sending email. But all her inbox email prior to any new downloaded emails were all gone. They were not in the “Deleted Items” box. I checked all boxes. She had no extra created folders.

What I found very odd is:  When I check the Personal Folder size it shows the total size as 1.8GB. However, when I go to the actual Outlook.pst file located in the default path, it shows it at 8.3GB  in size. I ran the Outlook compaction and it made no difference. It still shows 1.8GB in Outlook and 8.3GB as the actual file size.
From speaking to the user and determining how much email she actually kept in her inbox, she stated that she had only 9 months of email. She knows that she has less email in her inbox then she has in her Outbox. Her current outbox size is 1.4GB in size

The Outlook was being backed up nightly using Mozy’s Online backup. When I went to their site, it shows the last 2 weeks of outlook.pst backups ranging from 7.9GB to the latest 8.3GB

So my fear is that there’s definitely something wrong with the big difference in the two sizes.

I created a new Outlook.pst file into a different location on her PC. I made this new file the “default” outlook folder
In Outlook, I moved over all the contents of the older folder into this new folder. Now when I look at the total size of Outlook in both places, they are near identical as they should be.

Is it possible that there’s a hidden feature in Outlook that hides email of is it caused by corruption of some sort. Any thoughts and/or ideas would be appreciated.