TouchUI: Alert "It seems like you are trying to edit an external site. We will redirect back to the referencing site." when editing from a friendly URL in AEM

When editing a page in an author instance with a host name (mysite.com) in the URL other than the author's instance host name (that is, host:port), the message below is seen: 
It seems like you are trying to edit an external site. We will redirect back to the referencing site.

Environment

AEM 6.2 Sites

Resolution

There are two workarounds:
A. The operation can be performed successfully by opening the same page in a new tab. cmd/ctrl+click the link to open it in a new tab.
OR
B. Overlay [1] and comment out line 539 and 540:

[1] /libs/cq/gui/components/authoring/editors/clientlibs/core/js/ContentFrame.js