The specific events that led to this were:
- Ran south through the town (on horseback) and rummaged the bin by the noticeboard next to Sam's shop.
- Kept running south and ran onto the docks by the coffee shop, triggering Raj's first heart cutscene (where they talk about joining the committee)
After the cutscene ended, the Tiger Barb pop-up from the fish I'd looted from the bin rummage got locked onto me for the entire day. I went in and out of buildings, I went diving, I watched 2 more cutscenes (one with Suki and one with Paul) and nothing made it disappear. Even sleeping to the next day, it was still there!
After I'd made sure I got clips, I exited to the menu and went back in and it was gone!