I met a same problem last month. I borrowed 4 vido tapes, when I
checked my library card one day after I return those tapes, an office
lady told me that I still hold a tape, I told them it must be a mistake, they
just set a mark on this tape in my account, two days late, them told
me they found it, otherwise they want me pay back money for it ( $10 ).
I am afriad that the book management system must have some
problem, or the bar-code scan equipment get mistake. After this
lesson, I always ask for rechecking my account immediately after
returning any items in the library.