WordPress: All the Categories disappear after you change the URL

While working on a new WordPress installation, I came across an annoying "bug."

Every time my boss would change his mind about the location of a Category, I would go into the Admin -> Posts -> Categories and make the change.

Suddenly, the entire list of Categories would disappear!

I would go into the database manually and change it back and everything would come reappear. How strange.

So, I Googled the problem, which is not uncommon, and I got all kinds of answers.
However, what I discovered was that the problem was with a Plug-In.

When I disabled the plug-in the problem would go away.
Re-enable the plug-in, problem came back.

The specific plug-in I had been using was Restrict Categories, which is a nice option that allows the Administrator to keep Writers and Bloggers from messing up other people's work by accident or otherwise.

Unfortunately, the plug-in ties the category names / URLs to each user somehow.
So, if you make a change, then the Administrator has to go back in and redo ALL of the permissions again.

Such a pain, almost makes the plug-in useless (unless you never make any changes to the structure of your site.)

So, again, if you're categories disappear, try disabling the plug-ins one at a time -- especially plug-ins like Restrict Categories that deals directly with Category access or manipulation in some way.