What is happening here is, when the reading pane view is turned off and you single click the message, Outlook brings up the view of the message as full view instead of bringing the view to the right or bottom when you have it turned on.
What we want is the Reading Pane to be turned off and nothing to happen when you single click.
Also, here is the image from the instruction to turn of Mark as Read. There isn't Mark as Read here to uncheck. Even if there were you couldn't uncheck it because you would have to choose another option. Can you please give images on the fix for this and not just text. It would help solve this.
When you have Reading Pane hidden your message view does the below when you single click it. We do not want this behavior.