pdfpages, XeTeX, and transparency

Question

I'm using pdfpages to include a cover made in Inkscape into a PDF. The PDF has transparent objects.

When building with pdflatex, the transparency is kept in the final PDF, but when I build with xelatex, I lose the transparency in the final PDF.

My cover PDF is http://r.pinson.free.fr/calvary/pdf/cover_fr.pdf

and a MWE is the following:

\documentclass{scrbook}    
\usepackage{pdfpages}
\begin{document}
\includepdf{cover_fr.pdf}
\end{document}

which generates http://r.pinson.free.fr/calvary/pdf/test_pdftex.pdf with pdflatex and http://r.pinson.free.fr/calvary/pdf/test_xetex.pdf with xelatex.

Am I missing an option? Is there a better way to include PDFs in XeTeX, or should I maybe convert it to a PNG instead?

Edit: I mean a gradient, not transparency. The original PDF has a yellow gradient behind the word "ou", which does not appear in the PDF generated with XeTeX.

Note: When I build, I have the following warnings:

** WARNING ** Version of PDF file (1.5) is newer than version limit specification.

Maybe I should export the PDF as 1.4 from Inkscape before importing it with XeTeX?

Answer 1

I regenerated the PDF in Inkscape using PDF 1.4 and it fixed the problem.