dhclient.leases grows forever?

[Luke Dean]

I've recently upgraded to version 6, and I'm using the new dhclient.
It seems to be working happily, but I've noticed that 
/var/db/dhclient.leases.rl0 just keeps growing and growing, with new 
leases being added to the end.  Leases that expired several hours ago 
remain in the file.

According to the manpage for dhclient.leases, this database is supposed to 
contain only leases that are "still valid", yet the expiration time on 
many of them has long since passed.

Is there a bug, a misconfiguration, or am I responsible for setting up my 
own script for purging this thing?  I can't find any cron-driven script 
that cleans up this file, so I'm wondering if dhclient is supposed to 
handle this itself, and if so, when?