If you click on a world and click another, it will automatically start that world. This is very annoying as I was trying to delete my older worlds. I had to go into my saves folder and delete them from the actual folder. While not game-breaking, this is quite annoying and it would be wonderful to have it fixed.
Confirmed, I get this as well. At first I thought my mouse was playing up and it was double clicking but further investigation showed that the mouse was ok and this was a new bug.