Maybe just a problem with font color not set to a standard value?
The root cause of the problem is that we do not completely embed the fonts in the PDF-reports. For Adobe reader (etc). it seems to be enough to embed subgroups of a font, but for a bunch of mobile pdf viewers and google pdf viewer, the font has to be completely embedded in the pdf.
Disadvantage of the full embedding is the increase of the filesize (e.g. dejavusans ~ +300kB). But it seems to be the only way to make sure that the PDF is shown correctly on all devices.
Google PDF Viewer example:
Attachment: Embeds a given font completely (not only subgroups) - if the [fontName].z / [fontName].ctg.z is provided in the tcpdf/fonts directory.
OK I think approx 400k is acceptable for a PDF report, and worth it rather than the PDF being not viewable on google, iphone etc.
Utilities like pdftotext also require the complete font to be embedded, so this practice isn't uncommon.
fixed in