I took a look at the asm code produced by post 8 and I don't see anything that jumps out as being wrong, so I don't know why it's having a problem.

One thing I would change... get rid of this
Code:
    INTCON = %11000000          ' Enable GIE, PEIE, falling edge.
It's not a good idea to manipulate the enable bits until everything is setup.
DT_INTS enables GIE and PEIE right before it exits the INT_CREATE macro.

If you want to clear the INTEDG bit then just clear that one... INTCON.0 = 0