Grr, thought I had replied to this already but I guess it glitched out somewhere
Anyways, the gist of my big post attempt earlier was to say that I believe this was a change introduced a while back now for these non-stance forms. I noticed a similar thing happen on my druid when I was in sneak up mode and demon form mode on my warlock. All I could do was place the spells on the bar along with the normal ones but split up to aid in knowing the difference.
It's not just an nUI thing though as I am sure I tested it out without any addons to see if the problem still occurred.