windows snapshot with ram - rollback problem

hello,

we have some problems with windows 7 vm (not tested with others, yet).

we install and update the vms, do a snapshot with RAM included, while the machine is running.

when we rollback to this snapshot a few days later the vm is running much too fast.
its not only the clock which runs about 1 minute in 5 seconds.
every process runs too fast, like in somekind of fast-forward mode :)

so, do we miss something? should the described process work at all?

we use a 3 node proxmox 3.0 (pve-manager/3.0/957f0862)

thanks.
Kind Regards
Sebastian