Hi Bob,
I was thinking about your problem, but as much as I tried, I can't figure out a good reason for that behaviour.
Are there any background activities going on that could interfere with the pretty high CPU demands of MIR Pro? Virus scans, firewalls, network activities, power saving options, or (a wild guess) MIDI SysEx transfers ...? There must be some well hidden conflict somewhere as soon as ProTools is part of the equation, because you wrote that MIR Pro behaves correctly when used stand-alone.
Kind regards,
/Dietz - Vienna Symphonic Library