How do I make my window not semi transparent in xubuntu?

For some reason, sometime a window would become semi transparent. It is really irritating because I can't focus on what I am doing.

When I restart that program, when it launches it is not semi transparent anymore.

I am using Xubuntu 12.04.

Actually, there is this feature where scrolling horizontally on the system title bar would change the transparency of the window.

Scrolling to the left would increase the window's transparency while scrolling to the right would decrease it. I accidentally scrolled to the left on the title bar which is the reason I didn't notice it until now.

Check from system settings the Window Manager Tweaks . At the last tab Compositor , do you have enabled the display compositing ?