Slowness effect with /effect do weird stuff

Description:Using the /effect command to give slowness, from level 7 the player walks backwards and for slowness 127 it moves the player backwards very fast. The slowness effect on level 13 flips the screen upside down, and does it for some levels too...
Comments for the pictures: The first picture is how my character normally looks like. The 2nd picture is my character with slowness effect 13.
The 3rd picture is my character with slowness effect 14, its more understandable.