Disk space readout in Virtualmin incorrect?

This is by no means a critical problem or one causing any problems, just something I noticed. When I log in to Virtualmin it tells me: Local disk space 77.30 GB total, 6 GB used.

A df -k tells me: ~$ df -k Filesystem 1K-blocks Used Available Use% Mounted on /dev/sda1 81054244 2207680 74761640 3% /

Since I am only using a little over 2 gigs why does it report 6 gigs used?

This is running on an Ubuntu 8.04 server os.

Thanks!