panic during install

Hello,

i hope this is the right place for this. Just after sysinstall wants to extract 'base' in the / dir, i get a panic (FreeBSD-beta2):

panic: Bio already on queue bp=0xc19e24a4
cpuid = 0
KDB: enter: panic
[thread pid 40 tid 100029 ]
Stopped at kdb_enter+0x2b: nop
db>

and I'm left at the debug prompt. 

I installed this in vmware. I already had quite a few 'generations' of FreeBSD on this system (not vmware, but 'real' systems), but this is the first time it's panic-ed. 

It is repeatable, so if there's something i can do in the debug prompt to provide more information, i'd gladly provide it.

Options I had:
I had 1 partition of 1G, no swap device (but 192MB for the virtual machine), and soft-updates was ON. 
When there was swap space available, the same thing happened. 
When Soft-updates was OFF, the same thing happened:

panic: Duplicate free of item 0xc1b035ac from zone 0xc143f000(g_bio)

cpuid = 0
KDB: enter: panic
[thread pid 40 tid 100034 ]
Stopped at kdb_enter+0x2b: nop
db>

As said, further details will be gladly provided,

Wiger van Houten