tomasien: For some reason your comment is being marked as a [dupe], even though it's the only one of yours in this thread. There's another deleted thread[1]. What's going on here?
I started a thread on this the same time this thread started. When I saw this one rising to the top I deleted it - I thought duplicate submissions were supposed to get merged in automatically and counted as upvotes instead of separate threads but I guess that didn't happen. I copied my comment from there to here.
Generally they do, but its a very simple match by URL, so yours might have a tracking query param or something that you didn't strip (or it might have been a link to the blog post)
I checked, it was an exact match. It was weird - thanks for helping!