I have this same problem with Natty Narwhal, but only with certain monitors. I have a Dell Inspiron latop. When I plug it into a square Dell monitor, it will work fine. When I use a wider Dell monitor, I have this exact bug. A window of any size in the VGA secondary monitor will jump to the laptop's window on maximization, either by button or by drag.
I have this same problem with Natty Narwhal, but only with certain monitors. I have a Dell Inspiron latop. When I plug it into a square Dell monitor, it will work fine. When I use a wider Dell monitor, I have this exact bug. A window of any size in the VGA secondary monitor will jump to the laptop's window on maximization, either by button or by drag.