Upon deleting a subfolder in the content browser, your currently open folder displays many objects from other folders as well. To replicate:
- Create a new folder inside an existing folder (I created mine inside Blueprints)
- Name the folder
- Delete the folder
It does not necessarily have to actually have anything in it - I discovered the bug upon creating a folder by mistake. The display will return to normal if you navigate away from the affected folder and then back.