I'm often finding myself very busy, and leave a few items as 'unread' in a feed to come back to later. However, when I update the feed, I get a lot of new unread content at the front. When I've read through these new headlines, I often want to mark a large section of Unread headlines as 'Read'. However, if you click on one item, it immediately becomes 'Read', and when you then click on the far item with the Shift key down, the far item becomes 'Read' as well, but it and all the Unread items between are now highlighted. However, you cannot select 'Mark as Read' for this block, because only 'Mark as Unread' is allowed (due to the last item selected having already been Read).
The menu item 'Mark All as Read' is not an option, since you want to leave the unread items from earlier sessions as unread.
You can work around this by selecting an item, marking it Unread, shift clicking on the far item, and then marking that Unread, and now you can mark the entire block Read.
But this seems tedious. If more than one item is in a selected block, then context menu entries appropriate for some of the items in that block ('Mark as Read', for example) should be selectable.