Hi Florian,
From my analysis, this is perfectly normal. For example consider this screenshot: 
You will notice that there are repeats, but only one MSKEYVALUE per "entry" which establishes the uniqueness.
You would also find that were it visible, all the entries of the same ExtMSKEY share the same MSKEY, which would also indicate that they are the same entry.
I'm not sure what you are querying after from this view, but you might want to consider a different view to search on.
Maybe Penka, Fedya, Ralitsa, or Plamen Pavlov can give us more insight. I don't recall if there is a breakdown of all the views in any of the documentation. If not, it would be a great thing to have!
Hope this helps!
Matt