The problem occurs when a user tries to make a copy of a private page. This has been reproduced on a clean install of 7.2.0 GA1.
Steps to reproduce:
Start up portal and log in as admin
Allow private pages for the default/current site
Create a child page for a private page
Select "Copy page" from created child page
Enter a name for the new page (eg. "Test") and click "Add"
The original page is copied
No page is copied, and the UI does not respond, no error message shown.
The error seems to rise from the method LayoutsAdminDisplayContext:getCopyLayoutURL(), where the "privateLayout" parameter in the resulting url evaluates as "false" but it should be "true". As a result the portal tries to copy a public page with the given id parameters, but will not find one.