Summary: The custom fields section of Schedule has a remove-field confirmation warning when you hit the "Save" button that says:
"Are you sure you want to remove field(s)? If yes, click 'Save' to continue."
This message appears if you removed a field, even if you then added it back and the "Save" button isn't going to remove anything.
1. In the Schedule tool, click on Fields.
2. Type fieldname "Weasels", click Add button.
3. Click checkbox next to Weasels field, click Remove.
4. Type fieldname "Weasels", click Add button.
5. Click "Save" button, see warning.
A user creating custom fields might make several add/delete changes before coming up with an arrangement they're happy with. When they hit the Save button they should only see messages about the changes that will actually be made.