Is iDentify doing this with every film, or just a majority? I've noticed with the free version of the application that it has trouble fetching the genre for about 80% of the content I throw at it, so I'm guessing this problem isn't exclusive to your version of the app.
You can always manually insert genres via iTunes, or even iDentify. In iDentify, highlight all films of the same genre and edit the tags in a batch, only editing the genre field when you do this. The same can be done with the current version of iTunes.