QComboBox inside QGraphicView has corrupted text

I've a QComboBox inside a QWidget inside a QGraphicView
Only on this computer all the text in the drop down of the
QComboBox look corrupted. I've tried to change the style, font, size,
bacground, color. Some characters look good but the text is corrupted.
I've no idea where to look to understand better the problem.
In the two attached images there are the correct version as it looks
on my developer machine and the corrupted version as it look on the other
computer.

I've a previos version of the software that used Qt 4.8.5 that works good