Hi,
Moving the mouse outside the Properties panel's frame, inactivates selected fields within which I was typing (inside the Properties panel).
This happens often when renaming a Sheet Title.
Thanks, John
You can control that with a setting in your Revit.INI file
https://knowledge.autodesk.com/support/revit-products/learn-explore/caas/CloudHelp/cloudhelp/2016/EN...