Horizontal ruler breaks the display of the WYSIWYG menu bar and toolbox

1) Steps to follow to reproduce for "Preview":

• Create a new page and go to edit mode
• Click "Edit in full screen"
• Insert Horizontal Ruler
• Click "Preview"
• Click "Back to edit"

Result: The full screen editing is broken (see attached images).

2) Steps to follow to reproduce for edit mode:

• Create a new page and go to edit mode
• Click "Edit">"WIKI"
• Write "----"
• Click "Save & Continue"
• Click "Choose Editor">"WYSIWYG"

Result: The menu bar and toolbox is not displayed (see attached images).