why does empty file /media/.hal-mtab-lock have suid bit set?

[Dave Burns]

I stumbled upon the follwoing:

#rpm -qf /media/.hal-mtab-lock
file /media/.hal-mtab-lock is not owned by any package

#ls -la /media/.hal-mtab-lock
-rwS-----x 1 root root 0 Jun 25 12:44 /media/.hal-mtab-lock

# file /media/.hal-mtab-lock
/media/.hal-mtab-lock: setuid empty

I find this strange. By googling I get the impression it is a valid
hald file, but why the weird permissions?

Thanks,
Dave