2.2.19 ipmaqs and private lans

[Jakub Ambrożewicz <ja@vigor.com.pl>]

Here is the situation

Private ----------- Debian --------- ISP
LAN                  eth1     eth0

Simple and clear. I used ipmasq package to do the job. 
And it worked perfectly with 192.168.0.0/24 network for
private lan. Then i switched private network to 10.0.0.0/24
and suddenly it stopped working. Not whole network, but
masquerading only. I still can ping from debian in both 
ways. I can even ping external interface from my internal
network. But i cant reach anything further. Packets aren't
denied and logged. They are simply gone. 
I set up simple masquerading with no firewall rules at all
with default ACCEPT on all interfaces and again it works
for 192... and does not for 10... Even simple forwarding 
fails for 10...
I tried it on potato box (i386) and woody box (celeron)
effects are the same.

Does anyone know what is the problem?
Thanks

JA