Here is what it does:
- When rendering an item which is duplicated in other feeds there will be an extra "Also in [feed]" header line for each feed with a duplicate.
- When changing the read state of an item with duplicates the read state change will be propagated to all other duplicates.
Well the current implementation does add the new duplicate as unread (leaving the older duplicated items as they are). This has the advantage of being noticed that the item was posted somewhere else. But depending on the spreading time of an item (maybe due to slow planet updates) this might be unpractical. Therefore please give it a try and tell me of your experiences!