Here's what we think is going on:

Whatever Forum you start an OMNI thread in (be it FT Miles, FT Travel, FT Airports, or FT Dining) is the Forum that "owns" it from then on. This is regardless of where you post a reply from. So, if I start an OMNI thread in FT Travel, and you view it from FT Miles, and even reply to it from there, you'll still end up in Travel's OMNI.

This is a side-effect if using a single OMNI across multiple Forums... When UBB starts a thread, it creates an HTML template based on the Forum you started in. This template wraps around the actual post content and stays with it from then on. There may be a chance that when we update threads across all the boards (which we haven't done too much lately, due to the increase in performance) that the ownership will change, but I doubt it. Of course, the next time we update, we'll see...