[pluggo] Pluggo issue : PT7.3/Instrument Tracks/XPSP2

Just wanted to check if I've missed something subtle (or not so subtle) on this:

If I create an instrument track in PT7.3 and insert a Pluggo synth, it doesnt respond to MIDI on that track.  Ive checked, and swapped out the Pluggo synth for the Digi-made Xpand! synth that comes with PT, and when that's there, it responds to MIDI on the track without issue.
However the same Pluggo synth works fine the 'old' way, using separate MIDI and audio tracks with the plugin as an insert on the Audio track.
Doesnt matter which Pluggo synth it is, none seem to work properly on instrument tracks.

Any thoughts, or pointers to something Ive missed? Ta.