Bug: Incorrect usage being reported in Webmin

I'm not sure if this is the right place to report this, but my Webmin is reporting incorrect hard disk usage in the main page when you sign in:

266.91 GB total, 17.42 GB used

However, that is not correct:

# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda5             2.0G  619M  1.3G  33% /
/dev/sda8             245G  870M  232G   1% /home
/dev/sda3             9.7G  1.7G  7.6G  19% /usr
/dev/sda2             9.7G  472M  8.8G   6% /var
/dev/sda1              99M   29M   65M  31% /boot
/dev/sda6             996M   34M  911M   4% /tmp
tmpfs                 995M     0  995M   0% /dev/shm

Any idea what could be causing this?