OpenVG paintings distorted in non-fullscreen mode of wince

Hi,
When I run the /example/openvg/star.exe with "-graphicssystem openvg", the star is distorted and scissored, as shown in the show.gif attached.
I also noticed by chance that when I changed the line 52 of main.cpp, from
mw.show();
to
mw.showMaximized();
things got better, but still stretched to bottom right. As shown in showMaximized.gif attached.
Then I changed the line 52 to
mw.showFullScreen();
It painted correctly as shown in showFullScreen.gif attached. Is it a bug of Qt in non-fullscreen mode?