Enabling blackhole causes problems

When I add the following lines to /etc/sysctl.conf:

net.inet.tcp.blackhole=2
net.inet.udp.blackhole=1

And I reboot, it will hang right before the login manager. At that point, I 
need to press Ctrl-C (closes  /etc/rc.d/localpkg) and I can boot normaly 
except that kmail will freeze when I try to read a message. I can't find the 
logic in that, but when I reboot without the 2 lines, it will boot and work 
fine.

I don't really need blackhole but I was curious to see if I could benefit from 
it.

Here's rc.conf:
ifconfig_sk0="inet 192.168.1.100 media 100baseTX mediaopt full-duplex netmask 
255.255.255.0"
hostname="clk01a"
defaultrouter="192.168.1.1"
linux_enable="YES"
ntpdate_flags="ntp1.cmc.ec.gc.ca"
ntpdate_enable="YES"
sendmail_enable="NONE"
samba_enable="YES"
lisa_enable="YES"
sshd_enable="YES"
usbd_enable="YES"
apache2_enable="YES"

and the ending of my bootlog:

Additional routing options:.
Starting devd.
Mounting NFS file systems:.
Creating and/or trimming log files:.
Starting syslogd.
Setting date via ntp.
23 May 11:50:50 ntpdate[282]: adjust time server 199.212.17.15 offset 
-0.066166
sec
ELF ldconfig 
path: /lib /usr/lib /usr/lib/compat /usr/X11R6/lib /usr/local/lib /
usr/local/lib/compat/pkg
a.out ldconfig path: /usr/lib/aout /usr/lib/compat/aout /usr/X11R6/lib/aout
Starting usbd.
Starting local daemons:.
Updating motd.
Configuring syscons: blanktime.
Starting sshd.
Initial i386 initialization:.
Additional ABI support: linux.
Starting cron.
Local package initialization:Starting apache2.
Starting lisa.
 rtcStarting SAMBA: removing stale tdbs :
/var/db/samba/messages.tdb
Starting nmbd.
Starting smbd.
<hang right here>

Is blackhole dependant of an option in the kernel? Do I have to have ipfw 
running?

Thanks,
Nicolas
-- 
FreeBSD 6.0-CURRENT #2: Sun May 22 11:29:47 EDT 2005     
nicblais_at_clk01a:/usr/obj/usr/src/sys/CLK01A 
PGP? : http://66.130.198.54:8081/security/nb_root.asc