Another really clunky thing I noticed right away is that there's a huge difference between viewing a sub through your home instance vs its home instance, in that you're no longer logged in when using the remote instance's URL, and there's no obvious way to get back to the corresponding location on your home instance. This means, for example, that when someone posts a link to another thread, it's always kind of broken for remote users.
I feel like something could be done to ease interoperability using the same techniques ad trackers use.
I'm especially baffled as to why the UI had a dedicated button to view content on its home instance. I can see how that might be useful in some circumstances and it would make sense to have it hidden in a menu, but I think it's just a confusing distraction for new users who typically have no use for a crippled view of what they're already looking at.
I had the same thing happen to me this morning also. Very confusing as a new user.