The hint for "dachu" tells that it is in locative. First, what is the locative case, and second, why is it used here?
While 'dachu' is genitive, it is also locative AND vocative (both singular). Yes, I know how genitive is taken in negation (nie ma dachu), but there must be some reason that locative is instead given in the hint. Either that, or it is simply a hint-error. We should try to report it next time we can.
When I check the word dachu it says it is locative, not genitive, as I supposed it to be.
Does "dach" come etimologically from the German word "Dach", also meaning roof?