Webkit 2.0 WebView does not play html5 video element

I am using Qt5.2, Webkit 2.0 on Windows 7. No problem on Linux Mint.

To reproduce:
1. Just compile the browser example and go to the following websites and try to play the videos in the browser.

http://www.w3.org/2010/05/video/mediaevents.html
http://www.videojs.com
http://sublimevideo.net/demo

The video actually plays but it is not visible. The audio is played and can be heard. If you click on the full-screen button on the controls then the video shows up full screen and is visible and plays well.
Also, in the normal mode( not full-screen) the the time-line of the video shows up as a blue line extending beyond the video size and even beyond the right boundary of the browser window itself.