Rollback a Rollback does not work as expected
Actually making a rollback does not rollback to before or after the rollback.
It rollbacks to a state that was targeted by the rollback you actually want to rollback
( R1 rollback before E1, R2 tries to rollback to before R1, in fact it tries to restore further before E1)
In fact, The commit linked to the rollback event is not the good one, actually it's the one we rollback to (so before E1 commit) instead of being the actual rollback commit (R1)