Structured view is replaced by Image view
A Document generated from a PDF using Poppler for instance may have troubles to be displayed in the docview.
If the WebLab Document contains both Text and Image, it first displays the Text (as expected). But in some cases (explained below), the Highlighted page is quickly replaced by a small view of the page.
Current MediaViewerService only checks the presence in the document of a native content with an exposed as and a format associated. As a a result, if a service tries to better describe the images generated by poppler (which do not have associated format), it could not be opened in the DocView.
The dc:type of the Document could probably be a good hint (dc:type is media for image, video and audio). And not for other documents.