I have a long thread in my group that started awhile back. I added a couple of hashtags to it yesterday, and this morning, several messages were added to the thread. Later on, I was screwing around with merge and split, and now, when I look in message view, only some of the messages that are still (or again) part of the thread bear the hashtags when looking at message view. Yet they do bear the tags when each individual message is clicked on.
This could be another facet of the bug wherein message preview is not updated to reflect message edits. I don't know. It is similar in some ways.