Relatively teleporting an entity resets its Motion

The bug

When teleporting an entity using the /tp or the /teleport command, its Motion is reset to Motion:[0.0d,0.0d,0.0d].

How to reproduce

1. Place a repeating command block.
2. Enter the command

   /execute as @e at @s run teleport @s ~ ~ ~

   and set it to always active.

3. Summon any entity and notice it is not affected by gravity (or moving around).

What I expected to happen was

The entity should be unaffected by the command, because its motion should not be changed by the /teleport command, unless any coordinate is set to an absolute one,just like players.

What actually happened was

The entity stopped moving, because the teleportation resets its Motion.