It seems the check for duplicates is only performed for the root node of the hierarchy you are moving. Any child nodes which are duplicates aren't actually checked.

This results in two pages within the same space sharing the same title. One of these pages will effectively be "shadowed" under the other and cannot be accessed.

Workaround to get to the "hidden" pages:

• Edit the page that can be seen to use a different title
• The two pages should now have unique titles, therefore can be reference separately