How so I stop a line of code from inserting itself on a user's save?

Question

I've watched the user make their edits and they aren't doing anything I can see that would insert this piece of code:
. However, when we review the page afterwards, there's a paragraph spacing added to one of the panels which they didn't touch and in the panel they edited that code is suddenly there. It's invisible in the editor and just acts like a line that can't be deleted. What is this and how can we stop it?

A. M. Alfaro · Accepted Answer

Sorry, I see I wasn't clear. The page has several panels but the code only appears when a user deletes the first line of that specific panel.

We discovered today that the only way it doesn't happen is if one goes directly to the Source Editor to make their deletion. After applying that change, any other changes can be made in the Rich Text Editor.

To me, this is not ideal because it shouldn't be happening. If it should, it would happen in every panel every time the first line is deleted.