hi, when playing animation hair is changeing why :S

hi everybody, i am try learning blender so i make a very simple animation for displacement map test. so i was trying it thinked how look hair so use hair sytstem but dont use vertex grup for density. and i use mask map with material so i was render it little bit and looking hair changeing :S :S

so problem is looking in this video. i was copy twice render images because i stoped it when see problem in hair.