Use this command while sitting on a ridable entity:

/tp ~ ~10 ~

Expected: you dismount and your X and Z coordinates don't change.
What happens: you dismount and you are moved by one block (same rules apply as when you dismount by pressing shift).

Old description:

When you ride a horse/minecart/pig ... and perform "/tp @e[r=3] ~ ~10 ~"
your X and Z coordinate will be subtracted by 1.

Relates to: MC-69254