Following XML would fail :

    <disk type='network' device='lun'>
      <driver name='qemu' type='raw'/>
      <source protocol='iscsi' name='iqn.2013-07.com.example:iscsi/1'>
        <host name='example.com' port='3260'/>
      </source>
      <target dev='sda' bus='scsi'/>
    </disk>

With the message:

error: Failed to start domain iscsilun
error: Unable to get device ID 'iqn.2013-07.com.example:iscsi/1': No such fi

Cause was commit id '1f49b05a' which added 'virDomainDiskSourceIsBlockType'