Grammar and auto correct in Norwegian

I have my iPhone language set to Norwegian

and although the grammar and auto correct software is generally very good, I

have noticed that there are some words that are grammatically correct which it doesn’t

recognize as grammatically correct and that the software sometimes autocorrects

a correct word into something which isn’t correct. One could say that this

happens because Norwegian is a small language, but the spelling software in

Microsoft Word does not have these faults so I wonder why the software behaves

in this way? It frustrates me that the software isn’t based on the correct

grammar.