The standard Lotus template does not refresh the view when switching to show unread only. In both templates, the preview pane does not mark the documents as read when the view unread only option is enabled.
But in the OpenNTF template, the show unread/show all actions refresh the hide the hide-when formulas. This apparently causes the view to refresh and hide the newly read previewed doc (but only when the user preference to mark previewed documents as read is enabled).
This may be fixed by creating a label formula (instead of having 2 different labeled buttons) and change the logic of the action to toggle between showing unread only and not (instead of having 2 buttons), no refresh required (I think).