Hmm.. Yeah. We haven't had layout of splitscreen and third person on second machine. Last time the second player on host machine had to leave first and the problem still existed, but when only two of us were left on separate machines the problem didn't occur anymore.
Non of the characters played on second machine have summon skills, so we haven't had possibility to notice how the hotbars behave with them. Second character on host machines has always loaded the hotbars correctly (even for the summon).