I needed my "little key" today

I had always assumed that I probably wouldn't need the little metal key inside my key fob until the battery in my fob died. Well, this morning I needed it and the battery in the fob was fine.

I parked in the dentist parking lot and as I was getting out of the car, I pushed the door lock button on the inside of the door, as is my usual habit. When I closed the door the seatbelt got caught in the door, so it didn't shut completely. The door had closed around the latch post, but wasn't completely closed. I tried to open the door by pulling on the handle, but it was locked, and didn't unlock as usual when I put my hand inside the door handle. I heard a longish beep, but that's it. I tried again with the same results. Then I tried pushing the button on the outside of the door handle, but I just heard the same beep again and the door didn't unlock. I walked around to the passenger side and tried to open the door over there, both by putting my hand in the handle, and also by pressing the button, with the same results. Then I pulled the key fob out of my pocket and pressed the unlock button on the fob. More beeping, but the doors wouldn't unlock. At that point I had no option (that I could think of) other than removing the small metal key from the fob and unlocking the door that way, which worked fine.

Has anyone else experienced this? An engineering glitch in the Prius, or was it in some sort of lockout mode?