Adding/removing rules - works from stdin, not from file?

I want to add or delete some rules to the active filter set on the fly from
command line, without changing the /etc/opt/ipf/ipf.conf file.
When I type the rules directly from terminal, like here:

# ipf -f -
<type rules here>
ctrl-D
#

the rules are added, but when I put the rules into a file, and type:

# ipf -f filename

or type something like

# echo '<rule text>' | ipf -f -

it doesn't work - "ipfstat" shows that the filter rules are unchanged.

Is it a bug or am I missing something?
Regards,
Jaroslaw Rafa
raj@ap.krakow.pl