Scan line under the icon bar

I have an LG Flatron IPS235 22" monitor, used almost exclusively with a 1920×1080 mode. Just today I noticed that I could see a single line of pixels below the iconbar. Not knowing exactly what was going on I tried playing with the Display application next to the Taskmanager, and changed from a 60Hz framerate to 50Hz.
No more pixels below the iconbar. I mention this just in case somebody finds this information useful.