Iw as in a room with a lot of empty shelfs (like old shelf, dirty bookshelf, etc..) I walked by and suddenly my mouse showed me that one Old Shelf turned into a "Bookshelf". Using it gave me a recipe. I think it's bug cause that never happend in 1.0.6
Room definition error on my part; all the bookshelves are one tile left of where they should be. Fixing it!
Awww, why? Sometimes a seemingly empty bookshelf could contain a scrap of paper with a recipe, right?