domU-current "root device" not found with dom0-4.0_STABLE

["Joel CARNAT" <joel%carnat.net@localhost>]

Hello,

I have a 4.0_STABLE/xen release powering a few 4.0_STABLE/domU and a
Windows 2003/domU. I created a 4.99.55/domU from the standard install
kernel. When I boot the domU, the kernel does not find the "root device":
==========
xbd0: 10240 MB, 512 bytes/sect x 20971520 sectors
Searching for RAID components...
unknown type console at xenbus0 id 0 not configured
boot device: <unknown>
root device:
==========

The Xen packages are:
xentools3-3.1.2
xenkernel3-3.1.2nb1
xentools3-hvm-3.1.2

Is this a known issue ?
If I manually enter "xbd0a" and <ENTER> for each other question, the domU
boot normally. The virtual partition is FFSv2 (if it matters).

Should I reinstall using FFSv1 or is there a tweak to have the domU
automatically boot ?

TIA,
    Jo