Moving message appears while page is copied by holding [Ctrl] key

Description

Steps to reproduce

1. Create a Page 1.
2. Copy Page 1 using the context menu and paste to itself -> subPage1 is created.
3. Hold the [Ctrl] key and select subPage1 to copy subPage1 -> Drag this page to its self -> subPage2 is created but its level is the same as the start page.
4. Hold the [Ctrl] key and select subPage2 to copy subPage2 -> Drag this page to under subPage1 ->subPage3 is created under subPage1.

Expected:
No moving message while copying pages.

Actual:
While subPage3 is copied by subPage2, a message appears:
*Moving the page in the structure will change the sort order of page "[Testing Page here]" to "According to sort index.
Are you sure you want to move the page?*

Note: This has happened since CMS 7.5.