I can now reproduce the horizontal lines on the top menu buttons' appearance and disappearance. If there's another application underneath Win Toolkit, they immediately disappear (which is what we want). If Windows 7's desktop wallpaper is the only thing behind Win Toolkit, then the lines appear. More specifically, even if the other application's transparent aero border portion is directly behind WT's buttons, the lines appear. Simply dragging WT away slightly can remove the lines.