Consider the following scenario:
- A user has 2 unread notifications for their User_talk page. Both of those notifications are in the "distant" past, so, say, they are in page 3 of the results.
- The page filter on the sidebar shows the User_talk page with [ 2 ] counter on it (correctly)
- The user is currently looking at the general local notification list, with "all" filter marked (so both read and unread messages show)
- The user clicks on the page filter on the sidebar, expecting to see 2 unread notifications
- Because the two notifications are buried in page 3, the user actually gets a list of read notifications, and they can't really see that the 2 notifications indicated are in the following pages, unless they click on the "unread" filter.
So, suggestion: It seems to me that, when clicking on the page filter in the sidebar, the user should expect to first see the unread messages that the filter refers to. In that case, we could state that a click on the sidebar loads the notifications related to the page but also changes the filter to 'unread'.
The user then automatically sees unread notifications first (relevant to their click) and they have the option to then click on "all" or "unread" if they wish to see all notifications that pertain to that particular page.