I can confirm it happened to me once too. In military base north of kamenka there are green watch towers. I climbed into one to overwatch while my buddies ware looting. After they finished i clicked climb down the ladder with action menu without even touching WSAD keys and my character did full sprint resulting in my death.

Flares and chemlights will be added to the game once they add physics and implement throwable objects. They will be in final game, don't worry.

Pretty sure its related to one of the balistic vests that are in the game (the black one that looks like bullet proof vest). The model on it is miss-aligned so the shoulders are too high, and when you go prone and aim down sight it gets in the way.