I also found yesterday that save indeed didn't works from mui apps in some conditions, reported, and Thore already fix it (it even was reported by Ken some days ago too): https://muidev.de/ticket/1No, the 'SAVE' does_not_work! Please read the very first message of this thread (and the headline of it - it says 'when saved').
MUI4 screenmode setting lost when saved from OWB
Re: MUI4 screenmode setting lost when saved from OWB
@Gregor
Re: MUI4 screenmode setting lost when saved from OWB
I really ask everybody to report bugs on the new MUI development site http://muidev.de. Get a login there and report all quirks, bugs and enhancement requests. I cannot read every post in all the different fora.