Moving Player-rided mobs using with /entitydata acts wrong

/entitydata @e[1201,63,-1160,dx=0,dy=6,dz=0,type=EntityHorse,tag=spawndeco_ready] {Motion:[-1.3d,3.0d,-0.4d], Invulnerable:0, Health:1.0f, Silent:1b, CustomNameVisible:1}

Used this command for move player-rided mobs with changing Motion tag. But it sometimes don't move correctly, it's critical for map makers.

Attachment 1 : Non-rided mobs are moving perfect

Attachment 2 (Youtube) : Sometimes player-rided mobs are moving wrong. https://youtu.be/76c610UrX2U