Data being cached? Doesn't reflect free space shown in System Settings.

Is Disk Inventory X's data being cached somehow? It doesn't reflect free space shown in System Settings as you can see from the attached screenshot. Additionally, there appears to be no way to force a refresh of that volume list, nor is it updated by opening the volume in question. I was down to that little free space previously, but cleared a lot of crap out (mainly by moving it over to that backup drive). Incidentally, I have restarted the app to no avail.