Comment 15 for bug 751605

What's also problematic here is that the window maximize preview is not on the display that the window ends up maximizing to.

Try this:
1. Put a small display (laptop screen) on the left, and a larger display (monitor) on the left.
2. Resize a window in the larger display so that it fills the display, but isn't maximized. It should be larger than the smaller display.
3. Clicking the window's title bar, drag it to the top of the smaller display, and notice that the maximize preview is on the smaller display.
4. Let up on the cursor, and notice that the window maximizes to the larger screen.

Then try this:
1. Put one display on the left, and one on the right.
2. Dragging a window by the title bar, move the mouse so that it is to the right of the border between the 2 screens. The window snap preview will show the window snapping to the left side of the right screen.
3. Without letting up, continue to drag the window to the right side of the left monitor. The window snap preview will not move.
4. Let up on the mouse, and notice that the window maximizes to the right half of the left screen even though the preview is on the left half of the right screen.

It was suggested in this thread that the desired solution is to "always maximise on the the monitor that contains the majority of the window at the moment the user gives the maximise command." I think it would be more intuitive to always maximize the window to where the maximize preview is, and make sure that the maximize preview is in the correct location. For the window maximize/snap preview, the behavior is to maximize the window based on where the mouse is, not where the majority of the window is. I suppose you could classify the second example above as a separate bug, that when you move your mouse between different snap locations the snap preview doesn't update even though the location that the window actually maximizes to does.