On freebsd 5, when you use a lot of bpf(4), and you stop using them, and
then you run something like /etc/periodic/weekly/310.locate , the bpf(4)
go away.
On -current, this doesn't seem to work anymore.

Fix: 

I don't have a fix, but revision 1.172 of kern/kern_conf.c looks suspect,
especially the lines:
%%%
+	if (dev->si_usecount == 0 &&
+	    (dev->si_flags & SI_CHEAPCLONE) && (dev->si_flags & SI_NAMED))
 	if (dev->si_devsw == NULL && dev->si_refcount == 0) {
 		LIST_REMOVE(dev, si_list);
 		flag = 1;
%%%
The indentation suggests that a line is missing...
How-To-Repeat: Use something like this:
#!/usr/bin/env perl
my $i;
my $s;
for ($i = 0; $i < 1000; $i++) {
	$s = "/dev/bpf".$i;
	system "ls $s";
}

and then run /etc/periodic/weekly/310.locate , the devices don't go away.