Most of my maps have placemarks with a variable number of years in the info window - this is an example page (takes a few seconds to load)
I recently looked at this page using IE9 and found that all the info windows with 3 years in their content wrap the third year onto a second line and have a vertical scroll bar. On the page above, I have temporarily replaced one of my usual "3" placemarkers with a pin placemarker so you can readily see the issue but you'll see the same scroll bar effect in the info window if you click on any other "3" placemarker on the map. On the other hand, for example, info windows for "4" placemarkers are fine - all 4 years are on the same line.
The scroll bar behaviour does not occur in IE8, Firefox, Opera or Chrome.