I've noticed that if you have 5 tags in your post that post only appears in the first tag topic but if you have only 4 tags than the post appears in all 4 topics.
4 tags: (I see my post in all 4 tags. I tested my theory with this post it orginally had 5 tags but I changed it to 4)
https://steemit.com/health/@wakeupnd/messing-with-genes-could-wipe-out-geniuses-from-the-earth
5 tags:(I don't see my post in any of the other tags)
https://steemit.com/news/@wakeupnd/gun-control-in-action-48-shot-11-fatally-in-christmas-weekend-shootings-in-chicago
It's possible 
Please comment if you know any more about this issue.
Thanks,
