Polyphony, Expression Maps, and Vienna Ensemble

I am having trouble getting Expression Maps to work correctly with the Vienna Ensemble (VE) player from VSL, specifically when using multiple voice (polyphonic) tracks in the notation editor.
For example, I have two flutes in one MIDI track, playing an octave apart, with each flute assigned to its own polyphonic voice in the Score Editor settings. The MIDI track is routed to an instance of VE which contains two instances of the Flute VST, on MIDI channels 1 and 2. The signal routing occurs correctly, with each instance (channel) only receiving the MIDI notes from their respective voices, but the Expression Map assigned to the track only seems to work for the first instance (channel 1), meaning I can see the patches changing in the matrix view.
But the second instance (channel 2) stays stuck on the patch all the time.
Any ideas?