Easton Press's "The 100 Greatest Books Ever Written"

How can I uncheck an item? I checked a book by accident and I have not read it. I already tried, a pop windows appears saying “Are you sure you want to mark this item as unconsumed” to which I clicked Ok. But then it is still checked as consumed. Any ideas?? Thanks. (oh by the way sorry this is not directly related to the easton press’s list)