XenServer virtual disks attach in wrong order

[Stephen Borrill <netbsd%precedence.co.uk@localhost>]

I'm running a 6.0_BETA PV guest in XenServer and have added a second 
virtual disk. In XenCenter this is shown as (approx):
pos name size device
0 root 10GB  /dev/xvda
1 test 1GB /dev/xvdb

However, the 1GB (/dev/xvdb) disk is mapped to /dev/xbd0 and 10GB 
(/dev/xvda) is mapped to /dev/xbd1.
xbd0 at xenbus0 id 51728: Xen Virtual Block Device Interface
xbd1 at xenbus0 id 51712: Xen Virtual Block Device Interface
[snip]
boot device: xbd0
root on xbd0a dumps on xbd0b

I guess this is related to:
http://mail-index.netbsd.org/port-xen/2012/02/09/msg007127.html

The id figures are 0xca10 and 0xca00 respectively.

--
Stephen