I don't use TT to create posts out of tweets. I only use it to send a tweet from a blog post. I'd like to include hashtags for these post-driven tweets.
What I'm noticing is that the hashtags I enter in the post-specific TT hashtag field are one post behind. That is, the hashtags for post #1 are appended to the tweet for post #2. Referring to the order of publication. Happened for me in 2.8.5 as well. I've just been observing closer now that I'm on 2.8.6 because so far it's been a weird problem that seems to only come up when I change the hash tags I want to use. It's annoying since I can't predict my hashtags like that.
If I'm doing something wrong please let me know so I can shape up.
Also, the 'default hashtags for posts' field form the TT options page always seem to be ignored. Haven't investigated whether this is related or not. Seems like it could be a symptom of the above issue, since perhaps the default tags are only checked when TT is determining what the hashtags from the post are, and if they're blank then the defaults take over. But since the hashtag determination has already been made by the previous post's hashtags (and I assume written to the DB), then perhaps the defaults are ignored, even though the hashtags could being a blank value. Total conjecture.