If a player taps the crouch key multiple times rapidly while holding the key to move forwards, this will often result in the character coming out of the crouch position and immediately beginning to sprint forward. This is, presumably, because each time the player stands, this is treated the same as if they just pushed to walk forwards, and tapping forwards twice is one method to begin sprinting.

I don't believe systems specs, game mode etc affect this issue, although I haven't tested this.