Filed as a follow-up per @Pppery comment - https://phabricator.wikimedia.org/T370981#10083439
Steps:
1. On betalabs wiki, as an admin go to Special:ManageMentors.
1. Click on the Edit button to edit settings for a mentor **with a custom introduction message**.
1. On Special:ManageMentors/edit-mentor/ [mentor userid] click the check box for **Is away?** status.
1. Do //not// modify the custom introduction message of the mentor
1. In the **Away until** field select any of the available days - click on **Submit**
What happened:
- the notice **"Your edit was ignored because no change was made to the text."** appears
- the selected date is saved
- the Away status is actually set.
- on is still on the Special:ManageMentors edit form for that admin
What should have happened:
- no notice appears
- The form is replaced with a basic message saying "Mentorship-related options for mentor XYZ were changed."
- (We make should that message nicer. Codex success message styles?)