This could be a driver issues so I would make sure your graphics drivers are all up to date. That said, while Windows (XP and newer) supports (for the most part) multi-monitors, not all programs do. And even the latest operating systems sometimes have little issues, and seem to get confused occasionally as to which monitor is primary and which is secondary. So a multi-monitor utility is almost a necessity. My favorite is
UltraMon – not free, but worth it. Others have suggested the free
DisplayFusion, but I have no experience with it.