startupPolicy issue when changing CD

Hi, when adding support for CD disk on block based storage into oVirt, I spotted following issue. When starting VM without CD, we add startupPolicy='optional' attribute into <source> element. Whole XML looks like this: <disk type='file' device='cdrom'> <driver name='qemu' error_policy='report'/> <source startupPolicy='optional'/> <target dev='sdc' bus='sata'/> <readonly/> <alias name='ua-d7003457-63c3-4c98-80f0-08ab5042c65e'/> <address type='drive' controller='0' bus='0' target='0' unit='2'/> </disk> To change/insert CD we use libvirt.updateDeviceFlags() with XML which looks like this (for block based disk): <?xml version='1.0' encoding='utf-8'?> <disk device="cdrom" type="block"> <source dev="/rhev/data-center/mnt/blockSD/cdac2a0c-b110-456d-a988-7d588626c871/images/638247d7-b4b1-4d98-87fa-c90235fcf4b1/145e7cd2-f92d-4eec-a8fb-6835b4b652e1" /> <target bus="sata" dev="sdc" /> </disk> However, updateDeviceFlags() fails with libvirt.libvirtError: XML error: 'startupPolicy' is only valid for 'file' type volume What is the reason for this error? We don't use `startupPolicy` attribute for block based disks, as shown on example above. Thanks in advance. Vojta