When creating a custom field, specifically in the "Create custom note for features" screen, typing in your desired name auto-populates the Key field with the same name + underscores. However, when I misspelled the Name field and corrected it, the Key field did not auto-correct.
Based on the auto-population of this field, I would expect this to stay in synch with the Name field until saved. That is when I adjust "Expected Behaviro" to "Expected Behavior", the key field should adjust from "expected behaviro" to "expected_behavior".
This certainly isn't required, but a recommendation to prevent users from essentially stubbing their own toe, as it were.