Order of ipf, ipnat and bpf

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

I'm alway confused in which order an incoming (or outgoing) packet is 
processed by ipf, ipnat and bpf.
What I observed is:
-- for a packet processed by an ipnat rdr rule, you, in an ipf rule, 
   need to use the re-written port number
-- tcpdump doesn't notice packets blocked by ipf
-- for a packet processed by an ipnat rdr rule, tcpdump displays the
   original port number.
I can't put the three in an order that explains what I observe.
Does a packet transformed by a rdr rule internally carry both port numbers?