Reboot after mount of already mounted disk

I'm running  7-Current built on 09/15 .
When accidentially trying to mount a NTFS disk that was already mounted, 
the system rebooted.
The message I got was: "lockmgr locking against itself."
I did this several times on purpose, with NTFS and EXT2 disks, with the 
same result.
UFS2 disks seem unaffected.