I was viewing messages in a thread. I posted message#1590857 . When viewing that message, if I clicked on the "Show map of thread" button at the bottom I got the first message of the thread rather than the map. This happened while it was the last message of that branch, but it also happened on the previous message.

UPDATE: ignore this, it's been a while since I used that particular function, on looking more closely I believe it's working as it should.