3D FlipBook - Multi language (Polylang) support/issue

Hi! I'm trying to use 3DFlipbook pro with Polylang. A book with main language Italian (PDF) and translated ones in English, French, Portuguese, Spanish, Polish (also PDFs). I experienced some problems adding the PDF file of translated books after the PDF in main language has been added. The translated PDF is correctly selected, but after I save, the PDF url and the thumbnail is related to the mail language book (Italian). If I select and save the translated PDFs before saving the main language PDF all have been saved correctly.