Dissector_add_uint_range and packet-ip.c

I have an experimental network which is running IP-UDP-IP-UDP-XXX. I've written a dissector plugin for the XXX protocol and used dissector_add_uint_range to bind it to multiple UDP ports (more or less like in packet-http). I also used prefs_register_range_preference to allow the user to specify the UDP ports. That all works fine.

I then went into the epan/dissectors directory and made the same modifications in packet-ip (using dissector_add_uint_range to bind ip_handle to a udp.port range). The call to prefs_register_range_preference seems to be working: the config page allows me to set the udp.port range. However, the ip dissectors are not called.

I can use "decode as" to force the second level of ip decoding, but there are a lot of ports to do this for.

Any thoughts on why the changes to the (much more complicated) packet-ip code aren't working?

Thanks, Greg