Unable to spread window over two screens
 

Ever since updating to 10.9, I have no longer been able to display a window across two displays physically placed side by side.

Any others have this issue?

Mission Control is the culprit
 

Maverick now enables the Menu Bar and Docking bars on each dosplay. As well, you can now set that each display is a separate 'Space' accessable through Mission Control. This seems to have resulted in making each display a completely separate entity, so each display works independently. When you move a window from one display to another, it displays it as if you had moved it off the display in a one display settup.

The advantages the new functionality gives is that there is now a Menu and Docking Bar for each display. This means you do not need a 3rd party app to hava a menu bar on each display, but does mean that you cannot have the one window spread over 2 or 3 displays. You can also set up separate 'Spaces' for each display.

If you do not want this new functionality go to System Settings->Mission Control and uncheck the 'Display have separate Spaces' option. You will need to re-login to have the setting applied.

Thanks for the hint.

While I liked the menus on multiple screens, I have some massive spreadsheets so I spread MS excel over multiple monitors so I can have multiple windows open at the same time. Unfortunately I need functionality of Windows version as well so that complicates things further.

Turning functionality off got things back to how I like to use.