Port forwarding does not work with ubuntu server 13.04

Port forwarding does not work with ubuntu server 13.04

I'm trying to run nodejs app in my ubuntu server, that is running behind
TP-Link router. Server is set up as DMZ host in this router, so, router
should forward all connection to any port to this server. There is apache
and ssh running and forwarding works fine. But no way to reach port 4000
for example. I'm using 0.0.0.0:4000 to create server, so I can reach it
via local network (as a 192.168.1.100:4000), but not from the internet.
There is a difference between ports 80, 22 and 4000 in netstat output,
that I don't understand:
tcp6 0 0 :::80 :::* LISTEN
17175/apache2
tcp6 0 0 :::22 :::* LISTEN
9476/sshd
.........
tcp 0 0 0.0.0.0:4000 0.0.0.0:* LISTEN
17196/node
It's only difference, that I found. Any suggestion why can't I use port
4000? Ubuntu server is just fresh installed, there was ubuntu desktop
before and were working well.