block device lock difference between netbsd-4 and netbsd-5

[Brad du Plessis <bradd%cat.co.za@localhost>]

Hi,

I've noticed this difference between netbsd-4 and netbsd-5:

netbsd-4:

# dd if=/dev/wd0d of=/dev/null &
[1] 5330
# dd if=/dev/wd0d of=/dev/null &
[2] 6390


netbsd-5:

# dd if=/dev/wd0d of=/dev/null &
[1] 25717
# dd if=/dev/wd0d of=/dev/null &
[2] 26592
# dd: /dev/wd0d: Device busy
[2]    Exit 1                        dd if=/dev/wd0d of=/dev/null

Why the difference? Is there anything I can set (like in my kernel 
config file for example) to prevent the locking in netbsd-5?

Thanks,
 Brad