I don't think I'll need access to your server for this issue. I was able to replicate it on a VirtualBox install. Do the following and tell me when you have a chance if this solves the issue.
apt-get install -y linux-image-extra-virtual
service quota stop
quotacheck -auMF vfsv1
quotaon -uv /
service quota start
In short it appears that the quota module was removed from the virtual kernel. If Kimsufi is putting their machines up via cloud images and other such "quick launch" measures, then this is most certainly the case. It would also explain the sea of 20 network interface adapters that Kimsufi uses.
I am going to implement this within the script on quota install on the next production release.
This may also help anyone else that is noticing diskspace not updating properly.