ABR11 Restore causes VM reboot in Hyper-V

I'm using ABR11 to convert a number of physical workstations to virtual PCs running under Hyper-V. Generally the process works fine but recently a strange problem has arisen during the restore procedure. Basically the Acronis software seems to cause a reboot of the virtual machine just at the point where you specify the location of the backup file. Occasionally it gets as far as starting the restore (although progress appears at 0%) before the VM reboots. Has anyone else seen this issue and if so do you know what causes the reboot and how I can get around it?