More disappointment. I found the disassembly code in MESS and isolated it in a test program. It seems to work just fine. This really isn't a suprise, since that code's been around for a long time, and disassembly is pretty straightforward for any machine.
So, the question remains: what the heck is going on here? Haven't a clue.
Rather then invest time debugging MESS, I'll just write that off and continue using code and disassembly analysis for my work.