I suspect that somehow a shortcut key or macro has become enabled, that opens the pane. The normal ones are Alt+R,R or right-click (or the Context key) +K. The first will hide or reveal the pane; it works like a toggle switch.

You may be able to disable the auto-appearing of the pane by using your original Office/Word disc. Go into the "Ad or Remove features and look around for a Research or Research Pane feature. I don't have mine available at the moment, or I'd look it up for you.