When you sprint (ctrl+move, alternate movement methods) your soldier doesn't stop when they spot an enemy. If you're playing on high speed this turns it into a realtime game of "can I interrupt movement fast enough". It's a well-intentioned feature as stopping on every single enemy can get incredibly tedious. But slightly gamebreaking if you're sprinting around with few spotted enemies to avoid fire.
Instead I propose that if you spot an enemy while sprinting, the game will set movement speed for the next step to be extremely slow. This gives players the option to pause in a timely manner when they see an enemy, while still automatically continuing if they do not interrupt movement by right-clicking.