Why i can only get 720p downloaded of Itunes Movies ?

I followed another discussion here regarding this topic and only did see some general responses, which are not solved the topic.

If i buy in itunes a movie with 1080p i can expect also download it for later view with this resolution. I can see a comment inside itunes the movie itself alread say (1080p, download 720p).

• I did make the right settings in my Itunes already, still 720p
• My computer and the mac mini are absolutley fine for play 1080p, no use still 720p

How i can get the "Mercedes 1080p" i did buy and not ending up with an "Nissan 720p" as soon i want to drive ?

Thank you

Andreas