When I use click and drag from Athena's sidebar to move a child category to become a top-level category, it's not removing the parent category. Upon making any change that triggers autosave, the category pops back to its original place.   Moving a category to a different parent category (or from top-level into a category) works as expected. It's only making a sub-category a top-level category that isn't. Opening the category and using the "Move to" option above the title to remove the parent does work.   I'm on Vivaldi browser. Haven't tested with any other.