If your in M mode or manual shift mode
and lets say your in fourth but then you don't downshift but slow down for a stop sign you will see that the M4 will turn to an M2 it will automatically downshift for you
Just like it is not good to come to a complete stop and then start the car in fourth

If you rev too high(something like 6200-6500rpm's) the car will switch automatically in manual shift mode like from M3 to M4

Another thing which you experienced is if you gas the car all the way down and lets say your in M2 at a stop sign the car will automatically shift to M1 becuase that is the gear that you get the most power and performance from and the car is responding to what you want it to do
It will do the same thing in any other gear
respond to what you want it to do
You want power it will switch up and down gears to give you it without your touch

If your in Regular Auto or D
If you count the gears as you accelerate at little or half throttle you will see that it will start in 2nd and go up the fifth
If you floor it, the car will start in 1st and then work its way up

If you are in Sport Drive or S D
the car revs much higher and begins in 1st
much more power from the higher RPM's
the car feels much faster

The car is not a stick and so the manual shift mode to me is nice and somewhat precise but horrible compared to a stick
The touch shift does not always respond when you floor it and when you do switch with it it switched anywhere from 250-750 rpm's over when you hit it
The worst though is when it doesn't respond
That is why I kinda hate it
I guess I suck at it

The Sport Drive on the other hand is a lot better
It's a lot of fun
It switches way higher in the RPM's and unless you have mastered the touch shift its much quicker

The regular Drive is regular and saves gas

This is what I think of my step
Hope I helped