Exch System manager wrong mailbox size

I have noticed that our exchange system manager on exchange 2000 sp3 on windows 2000 sp4 is misreporting the mailbox size of most mailboxes when compared to what outlook reports the size to be. We have a database that is about 14 GB, but the system manager is reporting a total of 6gb in size. I have looked at kb813880 and will be applying the patch this weekend. I will also run a isinteg to see if there are. Has anyone found any other reasons as to why system manager would report a bad mailbox size?

One final note. We have one mailbox that outlook reports a size for each folder that adds up to a lot larger then the size that it reports for the total size.

Thanks

Rod