Glyph width information is inconsistent in PDF

Hello,
i have recently updated my program from Qt 5.3.2 to Qt 5.6.1.
We are developing a software to design photobooks. In these Books you can, of course, also add texts.
A PDF is finally created to print the Book.

Since Qt 5.6.1 we get Preflight(PDF/X4 Check) errors in the resulting PDF (see https://www.dropbox.com/s/myu13v9ku7rbo1t/glyph_error.png?dl=0).
I don't know wich Qt Version Update causes the problem because we directly jumped to 5.6.1.

I have also a little example program where the error can be reproduced.
https://www.dropbox.com/s/t7ec8lo5lt8g0w6/glyph.zip?dl=0

Has anybody a idea how can i configure QPrinter or QPainter to avoid this glyph errors ?