Automatic owners, rough downshifts?

[RTW YARIS]

I havent had my Yaris long, and cant complain about anything except one thing in particular. With the automatic transmission, sometimes when coasting (especially noticable on downhill/declines) the transmission likes to downshift at seemingly odd times. I notice a lot of the time it will happen while coasting downhill and I very lightly begin to tap the brake. Its almost as if as soon as I touch the pedal, the transmission will drop a gear, thinking I am slowing down or coming to a stop even though I havent slowed down much, if at all. This results in the RPM coming up a lot higher than they normally would be while driving at that speed (not so much so that its banging off the rev limiter or anything, but its noticable). Anyone else experience something like this?