[Support API] [Bug] Merging Users is not atomic

I'm trying to merge two users, each with different emails and external_id. Say User_1 has email 1@ex.com and external_id 1, and User 2 has email 2@ex.com and external_id 2.

Immediately after that, I want to know the resulting user's identities. I would expect the answer to be two identities, one for the email 1@ex.com and one for the email 2@ex.com. But the API is only returning one of them.