When trying to configure IPX, I noticed that if I configure
it manually, and set up 802.2 or 802.3 frames, then the
ifup-ipx supplies ipx_interface with 802_2 and 802_3 as the
frametype instead of 802.2 and 802.3. ipx_interface churns
out an error message and IPX is not correctly initialised.
I looked at the code in ifup-ipx and there seems no attempt
to change the $interface variable (maybe a new version of
ipx_configure doesn't like the underscores?)

Hope this helps.