Renaming a folder can lead to files spreading in 2 folders

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-Create a folder (ie: "Folder") and copy inside it tons of files(ie: a big app or game).
-Try to rename the folder(ie: "NewFolder").
-Force quickly a refresh. Either with the refresh button of the Explorer window or via the right click menu.

If the content of the "Folder" is big enough:
-You will end having a "Folder" and a "NewFolder" with the content spread between those two.