I have never used categories before and was experimenting on a project that I had imported from Bib 7 into Bib 8.05.
I created some categories X, Y, and Z and played around with it assigning some references to these categories. Then I deleted categories X, Y, and Z and then tried to again make new categories with the same names X, Y, and Z. But Bib told me that those category names were already in use and did I want to give it a new name, but I had deleted that category so how could it already be in use? Anyway I kept the same names and low and behold they had the same references linked to them.
So I then deleted the category container and created a new one and tried to make new categories X, Y, and Z but Bib again told me that there were already existing categories with these names even though I had previously deleted both the categories themselves as well as the category container. And when I created categories X, Y, and Z all the previous links still existed.
So how do I really delete the categories so that I can reuse the names?