For Code Context, the behavior is a bug since the menu item check can be
changed independently of the actual status of Code Context.
As far as I can tell, flist.vars mostly contains variables created by
EditorWindow.py's "get_var_obj". A quick grep for ".vars" in idlelib can
confirm that.
It also contains variables created by PyShell.py, particularly
'<<toggle-jit-stack-viewer>>' and '<<toggle-debugger>>'. Since the
shell can only have one instance, its tkinter variables can be held
local to the EditorWindow instance.