i think the system is working as designed in this situation. i believe you didn’t disagree with the previous identifier’s ID. instead, you disagreed with the community taxon that existed just before your ID. so even when a specific prior identifier’s ID goes away, there’s no mechanism to also remove your disagreement, because these things are not linked.
to get the correct ID on the observation, just withdraw your ID. optionally, you could add the genus level ID afterward without a disagreement.
read more about disagreements here: https://forum.inaturalist.org/t/change-wording-used-by-the-system-when-downgrading-an-observation-to-an-higher-level-taxa/3862/60.