[REG 5.5.1 -> 5.6.0] Prints from Assistant are impossible to read

1. Open a documentation page in Assistant, e.g. "PaintContext Class".
2. Print this page.
   The printout is impossible to read.
   See the PDF-Document I printed using PdfCreator. Prints to paper look the same.

Printouts should be readable. With Qt 5.5.1 this works correctly.