Thanks for your reply. I initialy installed the beta from the download page, v2.1.0.432, then later when I had this issue I uninstalled it as per the instructions in the wiki, and installed v 2.0.0.420 thinking it might resolve things.
I'm trying to recall when this issue began, and think it may be related to removing a disk and replacing it with a larger capacity one, it failed to balance data across all connected disks. I then installed the 'Disk Space Equalizer' blancer thinking that would do its job, and thats where i am now.
Also in the GUI only Disks '0' and '5' seem to be displaying the amount of data corectly
Edited to add: One disk in this pool came from another PC also with DP installed, though I do think I formatted it before relocating it here, and adding to this pool.