We are using Moodle 2.8.7 and if I tell it to drop four of the students assignments, when you look at the user reports, on half of the students it will indicate the assignments that it has dropped. On the other half of the students, it doesn't. It looks like it's calculating correctly, so that's all that matters, but wondering what's going on.
Can you post examples from the user report (with names obscured) and the categories & items page? It's tough to tell what's going on without seeing.