>The problem turns to be more complicated, than I was originally thinking. In our framework we have a navigation buttons class, which has a combobox of available orders and a button to set filter.

This is why I like having a Viewing form and a DataEntry form called form the Viewing form either to edit the current record being viewed or adding a new one. It makes it easier to both View and Add this way if they aren't handled in the same process because they don't need to be and it isn't logical for them to be.