suspend VM to take snapshot

Hi, the question is not very critical but interesting for me. I have planned the backup of some KVM VM's on a proxmox ve 2.2 server. Backup mode is snapshot (VM's reside on LVM). The backups are OK but two of the machines (the same ones) are backed up with suspend. I see in the backup log the message "suspend VM to take snapshot". Then I see "resume VM" and then "VM is online again after 2 seconds."
Why have these two VM's to be suspended to make snapshot?
Is it possible to change something inside the VMs OS to make them backup without suspend? These VM's are running Windows Server 2003R2.