Huh.. That's a shame :(. Maybe what it refers to is if you had a branch on B rather than D, it might update that.
EDIT: Yeah, this seems to be it. `git branch b` on b, then `git rebase -i --update-ref @~3` from main caused branch ref `b` to move from d86229e to 02fcaf7:
* 1e354fb (HEAD -> main) fix b
* 40e6f70 c
* 02fcaf7 (b) b
| * f4188e0 (branched-feature) d
| * d86229e b
|/
* 5fe78fa a
EDIT: Yeah, this seems to be it. `git branch b` on b, then `git rebase -i --update-ref @~3` from main caused branch ref `b` to move from d86229e to 02fcaf7: