True story: I spend hours working on a several-hundred-piece model in Lego Digital Designer. When I load the saved model again, the program tells me it removed one brick that was misplaced. One brick. Out of hundreds. It didn't tell me what it was. It didn't tell me where it was. And I may never know, until I actually build the model in real life someday and discover that one missing piece was supposed to hold everything together. Such is life.