Resizing a column in the Grid Leads to resizing of the Grid wrapper along with the GroupPanel. The problem can be replicated with the following Resizing settings:

<Resizing AllowColumnResize="true" AllowRowResize="true" EnableRealTimeResize="true" ResizeGridOnColumnResize="false" EnableNextColumnResize="true"/>

The issue occurs only on certain Screen sizes, or when the browser/display has some zoom applied.