Why does SharePoint 2013 Search append "text/html; charset=utf-8 " to some ContentTypes and how can it be avoided?

I have a question according the Search in SharePoint 2013. My Search does append some strange "Types" to the ContentTypes. For example Documents with a Content Type with the Parent Content Type "Page" have sometimes (not always) the prefix text/html; chareset=utf-8.

In the Picture: putting out some ContentTypes from the search including text/html; charset=utf-8 Article Page and Page

As you can see: a document with a Content Type with the parent CT Document is shown with the prefix application/pdf

My Question is: Why does SharePoint append those strange Texts and how can i get rid of them?