I then added the equipped pair to favorites, and assigned a single key to the set in the favorites menu. However, I tried the same thing with a pair of improved Steel Swords and they wouldn't appear as a single line, instead they appeared in my inventory as:
As a result, when I added them to favorites, only one would be equipped each time I pressed the hotkey, but pressing the hotkey twice does equip the second sword. I don't think this is a bug with improved weapons as I've seen it happen with normal weapons as well. The behavior is just inconsistent with regard to getting them to show up as "
It doesn't work like that though. If you have two different kinds of weapons favourited (ie: A steel sword with a fire enchant and one with a soul drain enchant) then they each get their own hotkey. My setup is often switching between a bow and dual daggers. I hit '1' to equip the daggers, '2' for the bow. I only need to hit '1' once to get both daggers equipped when i've got the bow drawn. HOWEVER. If you have duel daggers out and then change one of your hands to a spell, it breaks the dual wield association. From then on, you can't get both weapons out again without going back into your favourites menu. They're both on separate hotkeys and hitting one then the other just switches between them.
The other problem i've had with the hotkeys is with potions. If I have a stack of six healing potions in my favourites and I hotkey them, the hotkey randomly breaks. Sometimes I can use four of them, then it disappears, sometimes it vanishes after just a single use. There seems to be no rhyme or reason to it. They're all the same potion in a single stack. Very frustrating.

