From T244265#6592668:

(2) Attempting to assign the same mentor - the steps might be confusing for some users.

• On Special:ClaimMentee I enter two users - one I am already a mentor (ET2), and another I am not a mentor (ET207).
• click Submit

• click in the check box: "Yes, I really want to change the mentor" - click Submit

• at this point a user may be confused. There was no instructions to remove ET2 user and only then to re-submit. In fact, until ET2 will be removed, all other users won't be assigned a new mentor.

Adding some additional instructions to remove the users that are already mentees of the acting mentor will be helpful.