I seem to have stumbled onto a bug in IE where the scrollWidth is off by 1px compared to the offsetWidth. The trigger to this seems to be dependent on the length of the text/ch
Try to set the padding-right: 1px; for the class .base.
padding-right: 1px;
.base
.base{ font-size: 16px; overflow: hidden; padding-right: 1px; }