I didn't look at your code, but will remind you that interrupts 3-6 are change of state, and 1-2 are edge triggered (or something like that). The point is that any change on any pin in the 3-6 range will fire the same interrupt, where for 1 and 2 you get a different vector. I also remember something about cautionary tales about re-reading the status register. Maybe the real point is that I don't remember how they are different but 3-6 behave differently than 1 and 2, so dig into the PIC datasheet for details.
Also note that the rise time of inputs greater than 6 is different than for the first 6.
see
http://hacksaw.brush.googlepages.com/2006images for a picture of the signal.