I'm guessing an answer here...
I think window positioning might be more an OS function that an application function
My guess is that the OS may tend to remembers the position of each application window
Scribus uses multiple windows - main text, f2 & f3 palettes are all windows, Text Editor window etc
I THINK, but don't know for sure, that each window is positioned as an +/- offset from 0,0 of the primary window
so the OS likely "sees" a 2 screen system as one large screen, with windows offset from 0,0
I find I can dock the f2 & F3 palettes beside the main Scribus window and switch between f2 & f3 with a click on a tab
I've found curious behaviour when my system sleeps.
On screen dim, after a while the extension screen auto-powers off
When that happens, on wakeup I find all windows are relocated to the main screen & the extended screen is empty
- probably caused by the loss of power for the 2nd screen
If I wake up before that auto-power off, all the window positions are maintained.
spilly