Ubuntu: Some figures are not printed in PDF files?

It gets really annoying especially when there is no time for dealing with that. I have had this problem from time to time printing pdflatex or OOffice pdf files. Some images are not printed. The problem occurs when you have multi-layer image in your pdf (actually converting the image to pdf does not help). I must admit I don't have a time to find a core problem. Therefore, the simple solution is to flatten (merge the layers) the image. You can do it i.e. in Gimp.