Wow, that is really strange. I do not have answer yet but I have been unable to find the same situation anywhere. This happens when you go to Page Layout View but you are in Normal View. There is no protection in effect. Even stranger than the second sheet has Freeze Panes currently in effect but the button is grayed. I can just confirm that I am using the same OS/Office as you and see the same problem.

On the second sheet, if you go to Page Layout view, you get a warning that the panes are frozen, and will be unfrozen if you go to that view. If you say yes, the panes remain frozen and you stay in Normal view. So there is something in there pretty deep. I am tempted to say it's a corrupted file but I can't prove it.