When playing duels heroic mode I tried selecting the second hero power but when I started playing I still had the first/default one instead. This is after the latest patch, 19.2, before that I hadn’t collected enough cards to unlock the 2nd hero powers. At first I thought in my excitement to try them out I just hovered and read over the power without clicking it but it happened again in my next run.
Tested it in casual mode and got the same thing. The classes I used were hunter, mage (heroic) and warlock (casual) although I assume the same would have happened with any class