You can't be reborn to yourself because you don't exist as a sim to be reborn to after you are reborn.
Sim ghosts that pass on (lose connection with the world) are culled from the game and the family tree. It's always been this way unfortunately. You'd think they'd keep a remanent picture of that sim just for the family tree but it's not coded that way. Once a ghost sim is gone it's as if they never existed.
When your sim is reborn, their ghost sim self is culled, therefore no picture of your past self in the family tree. This is why so many generational simmers make and keep track of their sims family trees outside of the game. Not really a bug, just something that needs a serious overhaul.
