I am having the same problem right now. One screen for workspace and one screen for full screen playback doesnt seem to be possible. As soon as I am switching workspaces on my mac the host panels reset. Did anyone find a solution?? Thanks a lot!

Found it! You just have to activate every new workspace, deactivate host panels, drag everything in place and save the new workspace for EVERY workspace. Then it works.  

Oh no. After restarting the Mac and reconnecting the monitor it's the same problem again.. is there anyone who can help???

Yes unfortunately, if you disconnect the second monitor, it looses some of the Host Panels settings and won't remember what was where. It doesn't seem clear what it resets though.

What I ended up doing was to create a second set of User Settings - called "MyName 2 monitors" - in which all the Host Panels and Workspaces are meant for when I plug two monitors. Just have to remember to choose the correct User when I open the project.

Yuck. I just sat down to learn the new interface and the first thing I ran into was this problem. SO ANNOYING.