Confused about scroll limits...
 

When I look in my spell book under scrolls it currently says: 28(10) . I don't understand this. I know I have 28 scrolls, but is my limit 10? and, if so, how can I be over my limit? When I went to a store to buy a scroll, it said I can't because I had reached my limit. I'm confused. Is the some kind of bug? Thanks for any help provided.