User Categories disappear from tag browser

When I rename a category (that I created), an entire section of User Categories and their sub-category folder structure disappears from the tag browser. Some of the categories that I rename sit under a sub-category folder and some sit under the main User Category folder (ie: User Category main folder>Sub-Category folder>Category OR User Category main folder>Category). It's not just the parent categories that disappear but several user category folders also disappear. They are not hidden, meaning if I right click and choose "Show Category", they aren't in the list of hidden categories. However, I can get all of them back with their folder structures intact if I open Manage User Categories and simply click "OK" without doing anything. An oddity is that renaming the User Category main folder or sub-category folder does not cause this to happen - only the category itself.

There are 2 other User Category structures that do not disappear at all with the above renaming nor when I rename a category within them, so that's weird too.

Just wondering if there's a reason? I'm not losing categories, it's just a pain that I have to go into Manage User Categories each time as I'm in a process of adding the year to each category name that I've created.

I have added some pictures of my folder structure and when they go missing from view.

Attached Thumbnails