ok gang. I finally had a chance to test out & reproduce 'LIVE' (via Skype) the T4 polyphony issue with a good friend (in the UK) that owns a Tyros4.
While in A1 auto accomp mode, with split point set at F#2, I first had him select "Vocal Foxtrot" from the Ballroom Section, and Left Voice 'on' and assigned to piano, and RH voices 1, 2, and 3 all 'on' and assigned to different voices. Then he played a Bb7 chord in the LH, and then immediately after playing it, used the sustain pedal to keep it sounding, followed by playing both left and right hands together in the right section of the keyboard as follows: LH: D3-F3-G3-Bb3-D4 and RH: F4-G4-Bb4 (total 8 notes). When this was played there were no polyphony dropouts at all in either the style or the actual notes played on the keyboard. Only When 'one more' note (D5) was added to the RH chord to make a total of 9 notes played simultaneously, did a vocal dropout occur in the style. The moment the 9th note was taken out, the vocals in the style could be heard again.
I can only conclude that unless your playing style requires 9 notes played simultaneously in the RH section of the keyboard, this should not be a problem.
Additional note: It appears that only the Tyros4's new 'Vocal' voices were affected by this phenomenon, as no other voices within the style dropped out.
Scott
Scott Yee Entertainment