Zac was like that often, there are some things he just doesn't see the point of - like stacking dishes, he figured out what I wanted on the third attempt but he wouldn't repeat it for weeks no matter how much I praised him for it, he literally threw the dishes under the furniture, just missed stacking them dozens of times, and got worse not better. I thought he didn't understand... but he was just being too clever for me. In the end I accepted it for that trick. Look at this video I made of him tricking me, beating me at my own game and generally just being now like any of the "how to train" videos/books imply dogs are...
Zac is too clever and simply doesn't see the point of this trick. I call him an intuitive learner. But as I have built up a better relationship with Zac and he doesn't so much take me for granted he is happier to work. If you can crack one of the two problems the other will probably resolve itself.
Ooh I know that look!!! So funny and so frustrating!!