Actors when converted to spawnables are given a transform track, and the default position of doesn't seem to be saved to the template for blueprint actors. Compare the above behavior to a static mesh actor.
The actor has a transform track added to it which causes the origin offset to move it. Deleting the transform track moves it back to the world origin, not its original world position.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-164992 in the post.