This is indeed the case. And the reason is that the body itself is an extension of the soul essence of the original occupant. It was created and given a DNA complement that was a match to that person and their history, and the karmic issues needing to be addressed and, in particular, things to arise in the current lifetime. If you think about the logic here, they did not reincarnate as one of their offspring and carry the gene forward in that respect, even though somewhat diluted. They may stay in the light for a generation, and then come back in a new setting with other forbearers, and then the creation of a DNA complement that fits them would need to be done at that future point in time, and integrated with the ancestral contributions of the new parents in question, who may well be different from the preceding life. But in any case, the key is the DNA makeup, and the link to the akashic records established by the soul intending to occupy a given body. When someone wishes to leave and surrender the body to another being, the DNA remains the same and the link to the akashic records will still be in place. The brain and the subconscious aspect of the mind, as an extension of brain function, will still be present in the original body and an aspect of its existence.
So the walk-in moves into, in effect, a container outfitted for a different person, but has many aspects of that former occupant in the makeup of how the body functions, its memory traces, its beliefs, and the connection to the past history of the former occupant. The karma as well, is being expressed through the interaction with the akashic records and the cording of the body to the akashic record belonging to the former occupant. That will not change simply because the consciousness of that person has left the scene. So the walk-in steps into a troubled arena in many cases, because it will be, in effect, the life of a foreigner, many times unknown previously to the walk-in. And then, the past circumstances and difficulties of the person will be still manifesting as an energetic consequence of all that has happened previously, and falls to the walk-in to manage, take this on, and to rework things in order to acclimate and make the best of things.