Passenger door doesn't unlock when I open driver's door from inside

I believe the passenger side door is supposed to unlock automatically when I pull the inside handle on the driver's door to open it, but it doesn't (anymore).

I frequently put my purse, laptop bag, and whatever else on the passenger seat. In most cars -- and I swear in this car, before -- once I pull into the driveway and open the driver's door, the passenger door also unlocks. Not in this car, not now. And if the key is in my purse inside, it will not unlock from the outside. So the following dance happens very frequently:

1. Pull into driveway. Smart key is in purse on passenger seat.
2. Open driver's side door and get out.
3. Walk around to the other side.
4. Pull on the passenger door handle.
5. Curse.
6. Return to driver's side to hit the unlock switch on the inside of the door.

Can you confirm that this is not performing to spec, and suggest how to fix it? I've been through the manual and it's all about smartkey settings, but this seems to be about the automatic lock behavior only.

This is a 2009 Prius, just a hair under 100k, otherwise good shape.