If faulty grammar or spelling throws you out of a story, count yourself lucky not to be German. Things like that are standard. You learn to overlook them at first reading or you can't read anything at all. In books translated from English, especially children's or young adults ones, they tend to oversimplify the language, because.... young German readers are stupid???
We had a spelling and grammar reform a few years ago. As a result hardly anybody knows the new rules and people around my age or older are slowly forgetting the old ones. Everybody is making up his own set of rules and using it as they like in a mishmash of old and new. Yes, even in printed books, newspapers etc.