It was true on my ground water heat pump that I had in the past, Michael.
New thermostats can be programmed differently (even by the homeowner), but the general design/default is 2°F.
The auxiliary electric heaters are usually put on a separate circuit breaker, or in the panel are in the disconnect box at the unit. You can simply shut off the heaters there.
Also note: higher-end HVAC equipment has outdoor thermostats that prevent electric heaters from coming on if the temperature is higher than it’s set point. So if you’re wondering why the heaters don’t come on when you’re trying to turn them on, that is one potential reason.
For you brave souls out there, disconnecting the wire nut on the white thermostat wire in the unit will also prevent you from.
The only reason for the manual switch on thermostat is to make the unit run in the auxiliary heat mode only, without the heat pump running. If the heat pump is not running correctly and producing heat, the indoor fan will continue to blow nonstop and that is very uncomfortable. When you switch to emergency/auxiliary, you’re turning off the heat pump refrigeration and switching the auxiliary heat to the stage I on the thermostat, making it operate as a straight electric furnace.
Much being said that I still don’t understand and possibly because my units are older. Heat pump is around 10 years and the gas/propane furnace is original(1996). It’s always been a duel fuel system. Heat pump activates on “Heat” mode and the propane furnace on " Emergency Heat" but it’s strictly manual switchover. The thermostat is only a few years old, digital and programable.
After reading this, my take is that my system is outdated to the extent auto switch over was not an option at the time and can only be switched via manual mode.
Thanks for sharing!
I had a client recently that thought the E on the thermostat was for “Efficient” She hasn’t got the bill yet. 
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