So - for example:
Person A tweets "Anyone ever been to Ikea, what's it like?"
Person B (me) tweets back "Bloody lovely, yadda yadda" using the 'reply' link on their tweet
When I next go to my profile, I see "Bloody lovely, yadda yadda" as my last tweet, and I can click the speech bubble icon to see the tweet I replied to.
BUT - on Person A's tweet, my reply doesn't show up if I click the little speech bubble icon on their original tweet question - even though other people's replies DO.
This has happened quite a lot, and it doesn't seem to make any difference whether person A is one of my followers or not. TBH I'm getting a little paranoid