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?