I can't speak for the Prius, or any other vehicle, but the Owner's manual for the ES350 clearly states that the system might act strange if a second electronic key (FOB) is detected by the system. You can find this caution, from Lexus, on page 8 of your owners manual.
If you are lucky enough to have nothing happen when two keys are in the car at the same time, good for you. But I think it is worth noting, as I did in any earlier post, that if something strange is happening with your cars "smart access system" it would be nice to know what might be the cause. Use the information provided as you see fit, but it seems to me to be a bit inappropriate to state what might be the ES350 reactions based what a Prius' did or didn't do.
But then again I guess if you turn the wheel left in your Prius, and it goes left, it could be argued that its fair to state that the ES350 will also go left when you turn its wheel that way.