User blog comment:BertH/New VisualEditor now available in Labs/@comment-5558012-20131204024627/@comment-168424-20131209220749

Yes. This is a good idea and actually means the "Widen the Source mode edit box to fill the entire screen" checkbox is broken when the new Visual Editor is in use. The checkbox item should perhaps be disabled when the new Visual Editoris enabled until it works correctly.