There are many factors that can send a case to the wrong department, especially at the beginning of the game, as possibly some point in the work chain is working more saturated than others. Keep in mind that your precinct will work harder at first, and this could easily happen at earlier stages of progress. It is not so much a penalty, but a graphic way of expressing the workload. 

 

The goal is to minimize these inconveniences, and that will happen in more advanced stages of progress. Even if you have the correct department, all the work chain should be properly upgraded. This would take some time and patience!