Don't 'ya just love all those co-workers who screw the system and, as a result, conscientious people like you end up having to put in more hours and do that much more work?
My wife was put on a "temporary" job rotation, in which she was told to support another department in the company for half of her time. This put her in that department in the morning, and then she returned to her department for the afternoons. Turns out, the department which said they're short-staffed has plenty of people; it's just that a few of the folks don;t pull their fair share of the weight. They report late to work on a regular basis, spend the first 30 to 60 minutes each day bullshitting and/or going to cafeteria for coffee and breakfast. Meanwhile, my wife is doing their work!
I blame it on poor management and lack of leadership! In this case, the supervisor of the department my wife is helping out has NO BALLS, he's a wimp! I know this dumb-ass becasue I myself worked as a colleauge with him years ago. He's proabbly aware his people are scrwing the system, but he's "afraid" to do anything about it.