I am running Windows 7 and Display Fusion is up to date. I turned on the Span Window Across All Monitors button, but when I click it or use the hotkey for it, the window shrinks to its minimum height, matches the current monitor's width and moves to the top of the current monitor. See attached screenshot of what it did when I clicked the button while writing this post.

I have six monitors in a 3 across, 2 down configuration. I have not split them.

Thanks, that worked great!