The temporal reprojection which causes the trails is needed to make the technique work with reasonable performance (low volume resolution). Try it yourself - ‘r.volumetricfog.temporalreprojection 0’.
I think moving lights like flashlights / headlights need a completely different technique, which ray marches the shadowmap in screen space. Lots of games have done this - it was the standard technique before the Froxel Grid technique which relies on temporal reprojection. Unfortunately not something we are working on at the moment.