If the master pages section in the pages panel is collapsed, the menu item 'Document > View Masters' does nothing visually (except switch the focus from the currently selected page in the pages panel to the first master page).
I would expect that this menu item opens the master pages section.
The same applies to the little button at the bottom of the panel.
Edit: I notice that the main display also switches to the first master page. Perhaps that is all that is to be expected.
d.