It appears that this is a problem in RadDock, which is related to the fixed height of the RadDockZone controls: when you set height of a zone, it will automatically apply overflow-y:auto. This behavior is by design: the zone cannot increase its size when there are more docks inside and that's why it displays a vertical scrollbar. However, it seems that IE reserves space for the scrollbar, even when it is invisible. I can offer two solutions to the problem:
1) Set style="overflow-x:hidden;" to the zones
2) Use the MinHeight property instead of Height.
Let me know if you need additional assistance.
Valeri Hristov (Senior Developer, MCSD)
the Telerik team