@FediTips @geco_de Without feedback from @MastodonEngineering it's not clear what the proper fix is.
This might be a documentation bug, and clients are supposed to display all hashtags even if they are not in the content of the post.
Or, it might be a software bug, and Mastodon is supposed to remove additional hashtags provided by other software (e.g., Lemmy) if the hashtag doesn't appear in the content of the post.