If you are on a VPS by any chance, you will not find any of the advice on this forums useful.
When I had the quota problem, I went through all of the suggestions in vain.
No offense at all to those who were trying to help, I still appreciate the spirit of sharing.
The key lies in the 'quotaugidlimit' QOS setting in Virtuozzo. You need to check the 'Limited' option in the QOS thats it. No need to modify the fstab or anything else.
Hope that helps!
Cheers!