If you toggle the combat pace, you hold your weapon to the crosshairs and run a bit slower. If you press the RMB ( right mouse button ) to look trough the iron sights/ optics, you untoggle the combat pace as long as you are in the optics mode and runs with the normal speed ( no toggled combat pace ).

now with steps

1. go to edit mode
2. toggle the combat pace
3. walk forward
4. press RMB/ go to optics mode
5. now you should see that you untoggle the combat pace
6. press RMB another time/ exit the optics mode
7. now you toggled the combat pace

My description is a bit weird, but I hope you know what I mentioned. :D