Attached PDF is EMPTY when viewing it in confluence

After we upgraded to confluence 5.4.1 (we run 5.1 previously),
we run into a problem where some of our pages, where we had attached PDF files to, simply stopped rendered the PDF files, and instead an emtpy pdf is displayed. In 5.1 there were no problem to view the PDF files.

The PDF we are using are simply made from our printer, so it shouldn´t be any special about them.

To reproduce, simply add the attached PDF to a page in confluence with the view file macro.

In the log file the following line is displayed:
2014-01-16 13:34:40,384 WARN [DefaultSlideCacheManager:thread-1] [com.benryan.conversion.MemoryAwarePDFRenderer] drawImage Image of size 1656*2339 px dropped for memory protection