Well, if you look in QPdfBaseEnginePrivate::drawTextItem, you will see that a substituted font can have an unpleasant effect.

I've seen the two pdf's and I am not sure if this is a
font problem. The only way to see what's wrong is to take Acrobat Professional and PdfCan opener and examine/compare the page streams and resource dictionaries.
I would do that, but I'm on vacation( meaning I don't have Acrobat Pro at home ).

It looks more like when an unhandled exception occurs in code .

Regards