Upgraded my openvz vps with DA 5.8->5.9 with no complications. Working few days now, no problem.
Previously, quota utilities could not recognize the file system as having quotas enabled and refused to operate on it due to incorrect updating of /etc/mtab. This update prefers /proc/mounts to get a list of file systems with enabled quotas. Now, quota utilities recognize file systems with enabled quotas as expected.