Agreed, that's how AT works on Tyros too. Lean too hard on the left hand for too long and it can trigger AT across the whole keyboard.
On Tyros it doesn't make any difference to the issue if you have AT disabled to the left. The right voice AT's will still be triggered by the sensor (if they are enabled.)
[Could disable them temporarily if you wish and try "overplaying" the left hand again just to prove the point.]

john