Freeze while playing with unionfs

I was playing with unionfs (nearly everytime I do that I lose my uptime ;)).

I somehow managed to get the same unionfs mount from and to the same dir.

# mount -t unionfs -o copymode=transparent,whiteout=whenneeded,noatime 
bla1 bla2

both empty dirs; and after hitting some tab too much, my bash froze    .

Backtrace (shortened; each line was <func>() at <func>+0x<offset>):
sched_switch() +0xdd
mi_switch() +0x16f
sleepq_wait() +0x42
__lockmgr_args() +0x7bb
ffs_lock() + 0x8c
VOP_LOCK1_APV() +0x46
unionfs_lock() + 0x327
VOP_LOCK1_APV() +0x46
unionfs_lock() + 0x1ac
VOP_LOCK1_APV() +0x46
_vn_lock() +0x47
unionfs_readdir() +0x134
kern_getdirentries() +0x1fa
getdirentries() +0x23

I will reboot this machine in a few minutes; but I think this is 
reproducable.

-- Jille