Do you have the taskbar showing on both monitors? I'm not sure if this will work, but you can set your display so that the taskbar only shows on your 'primary' monitor. It's worth a try, just to see if it fixes the problem.
If you right click on the taskbar and select 'properties' you can play around with the settings. I haven't encountered your particular problem so far, it's still early days, hence my lack of knowledge regarding a quick fix.