i read the thread you started about that,
http://www.cherokeesrt8.com/forums/showthread.php?t=52171
after resetting the mil, by doing the short drives and cooldowns you completed the monitor drive traces. in your case, the pcm tested the secondary o2 sensors A-OK and did not trigger a mil while also leaving the sensors in a "ready" state. this led you to pass the obdII test.
more info on chrysler's drive traces can be found here:
http://img.neons.org/archives/chrysler_drive_cycle.pdf
as for the rest of us with headers & non-oem cats, the moment the emissions drive trace is complete and the secondary o2 sensors go "ready", the pcm triggers a mil due to not being able to test the sensors successfully.
to sum it up, if you reset the mil and go get tested, you fail due to the secondary o2 sensors not being "ready". but the moment you complete the necessary drive traces to mark the sensors ready, the pcm throws the mil, which gets you failed as well.
i'm not saying your account isn't true, but it is certainly atypical; no-one else that i know of has been able to duplicate your results. as such, it's not an account that people considering headers should base their decision on.