Opening a docx document in the rich text editor

I'm opening a Word (docX) document in the rich text editor, and it seems to open with none of the Styles from the original document in it.

So the document formatting looks strange: the default  font seems be called '"NSimSum", and heading are in 'Sitka Banner'.

This MAY be linked to a strage thing in the document.StyleDictionary. It doesn't like iterating through the StyleDefintions:

For example

for each Styles.StyleDefintion in document.StylesRepository

...does not work

dim firstStyle as Styles.StyleDefintion in document.StylesRepository.first

...is ok

so I am using:

            dim styleDef As Styles.StyleDefinition = document.StyleRepository.ElementAt(i)

...which is OK, but strange

Are these two things connected? Am I missing something ?

Thanks