The problems is most likely due to some global CSS style which is breaking the appearance of RadEditor. You should inspect the stylesheet of the problematic page and search for classes that applies padding / margin to TABLE, TR, TD, DIV, SPAN, UL and LI elements.
You can also try the solution provided in this article: http://www.telerik.com/support/kb/aspnet-ajax/editor/overriding-global-css-styles-inherited-by-radeditor.aspx
If you provide a live url to the page, we can examine it with Firebug / IE dev toolbar and find the problematic class.
the Telerik team
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