[possible bug] Page Editing strange behaviour

Tried twice, think is consistently behaving:
- open Page1
- open Editor on Page 1
- leave Editor window open
- change to another Page2 in Preview, using actual links
- in Customizer, Back
- now both pages are listed
- click on the other Page2
- Editor window still open, with text from Page1
- make any edit, Save
- Content from Page1 saves to Page2
  Not good :)
