You should place the proxy line before the portmap line.

`/usr/share/examples/ipf/mediaone' says:
# Make sure all the `proxy' lines are before any generic `portmap' lines, as
# the first match always wins.

> In my ipnat.conf, I've this:
> 
> map fxp0 192.168.34.0/24 -> a.b.c.145/32 portmap tcp/udp 40000:60000
> map fxp0 192.168.34.0/24 -> a.b.c.145/32
> # To make ftp work, using the internal ftp proxy, use:
> #
> map fxp0 192.168.34.0/24 -> a.b.c.145/32 proxy port ftp ftp/tcp
-- 
iKAWAMOTO Yosihisa!                   kawamoto@es.osaka-u.ac.jp