Snapshots though the sunstone

I use KVM + OpenNebula. I have a task to do automatic backups with the help of OpenNebula, and i thought that doing snapshots with schedule is a good idea. But in fact, after VM is poweroff’ed snapshot list becames empty. When i did it on VMware, it worked in another way)
Please, help find an issue for this task, cause i don’t see it now