When defining a new fieldset, even when it's empty the control panel editor still displays a Markitup content field. So this fieldset:

title: Custom Page

yields this: Screen Shot 2015-01-25 at 3.22.27 PM.png

Does anybody know where this phantom field is being defined or hardcoded? And is there a way to remove it or at least label it letting the user know to ignore it?

Answered by Jason Varga! Go to answer.