This is not something that is specific to us - this is something that is done by Virtuozzo - it rewrites network configuration files (including resolv.conf) upon VPS reboot
But as the node management you can indeed change this behavior (and should). After the initial configuration for a VPS, critical files should never be touched again by the vps software.
To fix this permanently on your nodes, simply edit the /etc/sysconfig/vz-scripts/[id].conf
and remove the NAMESERVER line.
Then the resolve.conf won't be touched when a vps reboots.
The reason why this is so important is that BIND cannot be replaced by NSD because you (okay, vz) inject 127.0.0.1 into resolv.conf - on smaller VPS the BIND memory size is too large. At a minimum 127.0.0.1 should be removed.