If you aim down sights and turn to run while pressing "space" to lower your weapon, you will be allowed to run a few steps, then run in place then the game will jarringly try to pull the scope back into view. Pressing "space" and clicking the right mouse button should both lower your weapon so that you can run. Having one button to lower a weapon from hip fire, and another button to lower from ADS is confusing. Both buttons should perform the same operation in game instead as it is "space" will fool you into believing you lowered the weapon as you run away but then you will be stuck running in place as the scope tries to go back to your view. Also, I believe sometimes this happens even if you do de-scope with the mouse. I'd have to try again in game to be sure.