The print option does not work properly in Qt Assistant. First I did not succeed to print at all:
0 - Open a help page
1 - click the print icon or select File->Print menu
2 - The print dialog opens

3 - Select print to printer and click Print
=> Problem nothing is printed

4 - Select Save as PDF and save
=> Problem no pdf file is created

Then I restarted Qt Assistant and I was able to print. However I encountered a seg fault following the steps:

0 - Open a help page
1 - select File->Print menu
2 - The print dialog opens
3 - Select Save as PDF and save
4 - the pdf file is created
5 - Select File->Print menu again
=> The application crashes (see trace in attached assistant_print_386.txt)