I was noticing some Rule 5 draft picks being released immediately after they are returned to their original team in my online league. I looked into it and it only happened when the export of the Player's original team was processed after the returning team.
What seems to be happening is the returning team sends the player to the player's original team and he is placed on that team's DFA list. Then when Player's Original team exported is loaded the player is released. I think he is released because he is not in the Original team's export file as being part of their organization. If the player's original team export is processed first and the returning team second the player is left on Team B's DFA.
I believe this has been happening for several versions of the game.