disk graph strangeness

Hello,

I've a host that's picking up all kinds of oddness on its disk graph.
The data seems correct, this is from client data:

[df] Filesystem 1024-blocks Used Available Capacity Mounted on /dev/sda2 1951832 659176 1292656 34% / /dev/mapper/root_vg-var 5242716 4405508 837208 85% /var /dev/mapper/root_vg-usr 2097084 1328888 768196 64% /usr /dev/mapper/root_vg-home 12582524 8865656 3716868 71% /home /dev/mapper/root_vg-varlocal 131067996 117865944 13202052 90% /var/local

but the graph looks like this:

I've never seen such bizarreness on one of my graphs. The last two lines are particularly creative. Any ideas how i can track this down?