Comment 3 for bug 1684506

Same.
After saving the qtconfig settings and reboot, there are two lines "fonts=" appears in ~/.config/Trolltech.conf

#after reboot
$ cat ~/.config/Trolltech.conf | grep font=
font="Ubuntu,8,-1,5,50,0,0,0,0,0"
font="Sans Serif,9,-1,5,50,0,0,0,0,0"

#after manual qtconfig saving
$ cat ~/.config/Trolltech.conf | grep font=
font="Ubuntu,8,-1,5,50,0,0,0,0,0"