1) When interacting with a shopkeeper, your inventory seems to become a secondary window, where as if you buy something or just browse, you can't interact with your inventory by browsing with your cursor (and with that I mean that you can't look at stats and what not), so you have to click on your inventory to make it primary and thereby be able to interact with it.

2) When you're walking and if the path is southward you can get stopped in your tracks because the UI is superseding and will override your actions. If I hold the left mouse button and it just happens to hit the UI, it will run to the last place the cursor was and you have to click the left mouse button again (and hold it, if that's what you want) to continue to move, and I have to say that in a game with a fixed camera position it makes it really annoying. I don't know if it was intended, but it's something that should be looked into!.