unable to mount root from USB

Hello,

today I updated my sources (CURRENT) and built a new system (world +
kernel).
But unfortunately, this action didn't end well 'cause I'm not able to boot
Freebsd
from my Maxtor One Touch USB HDD anymore.
Even booting from kernel.old doesnt't work anymore (tried everything:
normal, single user mode, acpi disabled/enabled).

Here is a short part of the boot messages (copied it manually):

##################################

usbus0: 12Mbps Full Speed USB v1.0
usbus1: 12Mbps Full Speed USB v1.0
usbus2: 12Mbps Full Speed USB v1.0
usbus3: 12Mbps Full Speed USB v1.0
usbus4: 480Mbps High Speed USB v2.0
SMP: AP CPU #1 Launched!
Root mount wainting for: usbus4 usbus3 usbus2 usbus1 usbus0
ugen0.1: <Intel> at usbus0
uhub0: <Intel UHCI root HUB, class 9/0, rev 1.00/1.00, addr 1> on usbus0
uhub0: 2 ports with 2 removable, self powered
ugen1.1: <Intel> at usbus0
uhub1: <Intel UHCI root HUB, class 9/0, rev 1.00/1.00, addr 1> on usbus1
uhub1: 2 ports with 2 removable, self powered
ugen4.1: <Intel> at usbus4
uhub2: <Intel EHCI root HUB, class 9/0, rev 2.00/1.00, addr 1> on usbus 4
Root mount wainting for: usbus4 usbus3 usbus2
Root mount wainting for: usbus4 usbus3 usbus2
Root mount wainting for: usbus4 usbus3 usbus2
uhub2: 8 ports with 8 removable, self powered
ugen2.1: <Intel> at usbus2
uhub3: <Intel UHCI root HUB, class 9/0, rev 1.00/1.00, addr 1> on usbus2
uhub3: 2 ports with 2 removable, self powered
ugen3.1: <Intel> at usbus3
uhub4: <Intel UHCI root HUB, class 9/0, rev 1.00/1.00, addr 1> on usbus3
uhub4: 2 ports with 2 removable, self powered
Root mount waiting for: usbus4
usb_alloc_device:1626: getting device descriptor at addr 2 failed,
USB_ERR_TIMEOUT!
Root mount wainting for: usbus4
Root mount wainting for: usbus4
usbd_req_re_enumerate:1553: getting device descriptor at addr 2 failed,
USB_ERR_TIMEOUT!
Root mount wainting for: usbus4
Root mount wainting for: usbus4
usbd_req_re_enumerate:1553: getting device descriptor at addr 2 failed,
USB_ERR_TIMEOUT!
ugen4.2: <(null)> at usbus4 (disconnected)
uhub_reattach_port:440: could not allocate new device!
Trying to mount root from ufs:/dev/da0s4a

######## [and the HDD suddenly shuts down] ##########

ROOT MOUNT ERROR:
If you have invalid mount options, rebott, and first try the following from
the loader prompt:

          set vfs.root.mountfrom.options=rw

and the remove invalid mount options from /etc/fstab.

Loader variables:
vfs.root.mountfrom=ufs:/dev/da0s4a
vfs.root.mountform.options=rw

[manual boot prompt]
mountroot> ?

List of GEOM managed disk devices:

Loader variables:
....

##################################

I hope this problem wasn't reported already, but I did not found everything.
This was not reported as a PR, 'cause I don't know if this is a real bug or
just my fault.

Regards,
Deniz