Problems with QWidget transparency

Hi, I am writing a class for Systemtray Notifications and I use background transparency (using QWidget) and does not work right. I did a small example to test if the same is happening on PyQt4, and I've found that there works as expected.

Code Example (in PyQt, which PySide is the same with the diff. imports): http://pastebin.com/QnmNvnfL

Result with PyQt4: http://postimg.org/image/8eybs17q7/

Result with PySide: http://postimg.org/image/xpnsnz8dd/

Any ideas?