libvirt users - Apr 2015 - can't boot from http cdrom

Hi. I'm try to boot from http cdrom and can't do that in case of scsi:
    <disk type='network' device='cdrom'>
      <driver name='qemu' type='raw'
cache='unsafe'/>
      <source protocol='http' name='/vps/rescue-4.5.2'>
        <host name='xx.xx' port='80'/>
      </source>
      <backingStore/>
      <target dev='sdb' bus='scsi'/>
      <readonly/>
      <alias name='scsi0-0-0-1'/>
      <address type='drive' controller='0' bus='0'
target='0' unit='1'/>
    </disk>

but in case of ide:
    <disk type='network' device='cdrom'>
      <driver name='qemu' type='raw'
cache='unsafe'/>
      <source protocol='http' name='/vps/rescue-4.5.2'>
        <host name='xx.xx' port='80'/>
      </source>
      <backingStore/>
      <target dev='hda' bus='ide'/>
      <readonly/>
      <alias name='ide0-0-0'/>
      <address type='drive' controller='0' bus='0'
target='0' unit='0'/>
    </disk>

all works fine.

libvirt - 1.2.10
qemu - 2.0.0
seabios - 1.7.5

-- 
Vasiliy Tolstov,
e-mail: v.tolstov@selfip.ru
jabber: vase@selfip.ru