I have two docs to either compare or take details from etc, I need them side by side, so I use the Window > Arrange option and have them in whatever config I need. They then resize to ⅔ the screen size next to each other. Then grabbing a corner to resize the window makes them jump all over the place. It works perfectly fine when I split a window (Window > Arrange > Split Window), it keeps the doc full size of the screen, so why not when tiling?