Just finished two flights in the C172 G1000. These were relatively short flights. I noticed the problem with the Heading Bug knob. At the start of a flight, the knob increases/decreases in one degree increments. After some time flying, it will only increase/decrease in 10 degree increments. On descent and approach, the knob will run away after just one click on the left mouse button. Using the mouse wheel you can contain changes to 10 degree increments.
I would urge you to submit a Zendesk ticket so that MS/Asobo are made a where that this is a widespread problem.