I've been doing a bit of research on MH this afternoon. Still haven't found an answer, so I thought I might appeal to the collective wisdom:
Problem: Every once in a while the default FSX ATC gets into (what appears to be) an unstoppable loop. here's how it goes -
JKM climb and maintain 8,000
JKM descend and maintain 7,000
JKM climb and maintain 8,000
JKM descend and maintain 7,000
JKM climb and maintain 8,000
Usually I don't let it go quite this far. I request higher (go for a big one, like +5,000). ATC will always grant your wish.