Let me see if I can describe the two issues with title-bar buttons:
1) I have four title bar buttons. On the furthermost button on the right, the program will not let me add a separator.
2) Now hen I have a separator on any of my title-bar button (except as noted above), I cannot move any of the buttons around. I remove the separator then the program will allow me to move the buttons around.
I forgot to mention that I am using the Beta 12 version of DisplayFusion Pro.
Ok, I see what the issue was with #2, moving the buttons, I had a separator between the two right most buttons, did not know that I had one there, and was trying to move the rightmost one. So your answer to #1 explains why this is happening.
So why not add a clear or 100% transparent icon that can be put on the right side to allow for space separators?.