This bug is in the new Department Heads assignment screen, when you click the assignments button next to a department head, it switches to an list of assignments for that department. Which is expected, however, sometimes if that list is long and has a scroll bar you are unable to scroll it and there is a small box with a minus sign "-" in it off to the right, floating by itself. Clicking this closes the assignment screen. You then have to reopen it until you don't get that "minimize" button.