High motion arrows display

execute @a[rym=-168,ry=-167,rxm=20,rx=21] ~ ~ ~ summon Arrow ~ ~ ~

{Motion:[1.36,-2.39,-6.43]}

This command summons an arrow with a very high motion. The arrow touched the ground in the right place (where my cursor was) but when the arrow was in the air, it had a weird motion and turned to the right.

I've recorded that (14 seconds):
https://www.youtube.com/watch?v=NAoxehEAVp8