You are correct. File a bug report with Apple via "Aperture➞Provide Aperture Feedback". My understanding is that the correct behavior is to have the Viewer show only the Stack Pick when the Browser is filtered by "Stack picks only".
"v" rotates between three UI states: Browser, Split View, and Viewer. The Browser displays the contents of the currently selected container(s), the Viewer shows the currently selected Images, and Split View shows one Browser and one Viewer at the same time. ("Visualization" means something different in English. It's use in place of "Viewer" introduces confusion.)