Right, looking at a lot of the Prestigio documentation, reviews, specs etc., the epubs should work fully.
I downloaded one of the free e-books from the Prestigio site, and on examining found that the directory structure inside the epub is non-existant. That is to say all files are in topmost level - and on examining the html, it was converted with calibre!
Edit: the file was
this one.
I've converted my testfile in calibre with the flatten structure option and as far as I can tell it matches the structure of the downloaded epub.
Can you now test this file, and report back.
Prestigio - Perkin.epub