Steps to reproduce:
Take page A and page B, blank pages both are parent documents and both have children. Renaming page A to page B results in page B having all children from both pages.
Have another two pages, page A - blank page and page B - dashboard, renaming page A to page B gives
"Error: A document with the name (page B.WebHome) already exists. Use a different name."
The same error is reproduced when renaming a dashboard page to another dashboard page.