Okay. I "Merged All Windows", but.....
There is no way to un-merge all windows.
Do I actually have to go in and "Move Tab to New Window" for every single tab?
MacBook Pro (13-inch Mid 2012), OS X El Capitan (10.11.1), Numbers
I noticed that as well. Obviously it's not a well-implemented "feature" (one that I don't really need).
Go to the Numbers menu > Provide Numbers Feedback & let Apple know that a way to "unmerge" windows/tabs is needed.