Why does is this happening
It’s not an error to have developer mode enabled. When you click on an option(Mac) and hover the cursor over a field, the field name will be shown.
It is just visible for few seconds only
No, when clicking option + cursor on the field then it will be visible!
No it’s not working
If you want to know child table field name open that row by clicking edit button .
Then hold Alt key and hover that field, you will get field_name.