I always thought the A/C button was used to run the A/C compressor, drying the air?
In the heatpump-equipped Leafs the A/C comes from the heat pump - there is no "A/C compressor" as a separate unit. When you select both heat and A/C you get heat from the PTC heater and A/C from the heatpump, which consumes the maximum amount of energy for a set temperature. I'm beginning to be glad that I don't obsess over energy usage graphs, because that display seems to be really confusing some of you.
Given the lack of complete info, it's pretty hard to know which mode is more efficient.
Does the heat pump's compressor run in heat only mode? If it does, then heat + AC seems to be more efficient.
You have a heatpump that uses the least amount of energy currently possible to provide heat, and just a tiny bit more energy than a dedicated A/C compressor to provide cooled air. You have a resistance heater (aka PTC) that uses much, much more energy to create the same amount of heat rather than simply move it from outside the car to inside. When you select Heat, both the heatpump and the PTC run at first, for maximum warming speed. Then the PTC throttles back or turns off, depending on the outside temp and the set temp inside. Once this happens, you are using less power to get heat than you would be using the PTC heater alone.
If, on the other hand, you select Heat and A/C, then the PTC heater runs alone to provide heat, and uses more power overall then the heatpump+PTC, because it can't throttle back as much. At the same time the heatpump is ALSO
running, to provide the chilled, dried air you requested with the A/C button (this doesn't happen at frigid temps, AFAIK). So unless adding chilled air to the mix somehow reduces
the amount of heat required (instead of increasing it, which is what happens*), you are feeding power to both units, which are then working against each other to provide the set temperature. This is as clear as I can make it. Stop looking at the damned energy use screen and look at the physics of heating, please.
* If your only purpose is to defog the windshield, then Heat + A/C can be more efficient if you run it only briefly and turn it off when not needed.