I have similiar problems with floating windows. Probably it's the same but I;m using those in other way.
I have float catalog window on second screen. It's working, but I have a lot of problems with it.
- with opened two catalog windows (one with all catalogs and second with my catalog with shortcuts) - sometimes when I open IC or open old project file, opened catalogs mixes themselves. It means - in first windows I still have all, in second - some other one and in IC window is docked new, third window with all of them),
- with open one floating catalog window, sometimes IC opens second docked.
Now I'm working with one floating catalog windowbecause it makes less problems, but posisbility to have opened more will be greatful.
On second screen I have also floating windows with "scene" and "properties" and they are always OK.