[PC-BSD Testing] PCBSD 8.1 does not boot

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I  have a desktop system with 4 SATA disks, ad4, ad5, ad6, ad7, running
FreeBSD 8.0, DesktopBSD, Ubuntu 8.10, and I have installed PCBSD 8.0 and
8.1.
The PCBSD 8.1 installation is fresh from today (using the USB stick
image). The slice ad6s3 was made by fdisk on Linux, the partitions
within this slice are default partitions as suggested by the PCBSD
install wizard. I also had the PCBSD boot manager installed and use
UFS+S file systems.

Here are the slices I use:

ad4s1	Linux boot   (200M)
ad4s2	PCBSD 8.0    (40G)
ad4s3	FreeBSD 8.0  (40G)

ad6s1	Linux boot   (200M)
ad6s2	DesktopBSD (7.2 based)  (20G)
ad6s3	PCBSD 8.1    (40G)

the other disks and slices are used as Linux mirrors and are not
relevant here.

I use Linux grub as boot manager. Here are the entries for the various BSDs:

1. FreeBSD 8.0
title       FreeBSD 8.0 on (hd0,2,a) ad4s3
root        (hd0,2,a)
kernel      /boot/loader

Status: this works

2. DesktopBSD
title       DesktopBSD on (hd2,1,a) ad6s2
root        (hd2,1,a)
kernel      /boot/loader

Status: this works

3a. PCBSD 8.1 first variant

title       PCBSD 8.1 on (hd2,2) ad6s3
rootnoverify (hd2,2)
chainloader +1

Status: system reboots immediately

3b. PCBSD 8.1 second variant
title       PCBSD 8.1 on (hd2,2,a) ad6s3
rootnoverify (hd2,2,a)
chainloader +1

Status: I see the FreeBSD menu:
F1  ?
F2  FreeBSD
F3  FreeBSD
F5  Drive 4
F6  PXE

when I choose F3 for PCBSD 8.1, the system "does nothing" (i.e. loops),
and with ctl-alt-del I reboot the system.

3c. PCBSD 8.1 third variant: I tried the same procedure as FreeBSD and
DesktopBSD use:
title       PCBSD 8.1 on (hd2,2,a) ad6s3
root        (hd2,2,a)
kernel      /boot/loader

Status: after the root command, it says
root        (hd2,2,a)
    Filesystem type unknown,
    partition type 0xa5
kernel      /boot/loader
    Error 17: Cannot mount selected partition
    Press any key to continue

and pressing the any key brings me back to the boot menu

The same status messages apply to PCBSD 8.0

How can I boot PCBSD? I might add that method 3a works perfectly well on
my laptop with an external USB disk.

Thanks and regards

Harald