Sorry, fellas, long day at work.
To leave feedback for a specific thread, you have to comment or post something within that thread. Otherwise the thread won't link back to you when you attempts to leave feedback. It also won't let you leave more than one feedback per thread. Let's say you purchase one of several items for sale from one individual thread. You leave feedback, then decide you want another item from that same thread. If you've already left feedback on the first purchase, you can't leave any for the second purchase. All you can really do is edit your first feedback to reflect both purchases.
If none of the above applies to your questions, then chalk it up to me being tired and blonde and maybe we can find another solution.