It might have happened to me too earlier using alexandrite UI on a world account. I can't be sure because I'm a zombie today with next to no sleep, however I replied to someone and it popped up on the wrong poster like 6 hours ago. This is highly unusual for me, even when extremely sleep deprived. I edited, and pasted the message appropriately. I have not seen the problem occur again since. I assumed it must have been me, but after seeing this post, I would say both are equally plausible; it was very out of character for me.