I have checked all embedded skins at the Editor demo page: http://demos.telerik.com/aspnet-ajax/editor/examples/overview/defaultcs.aspx
and all icons are displayed properly. From you screen as i could see, most probably you have some global CSS style applied to UL, LI that overrides and breaks Editor layout. If you have any custom CSS styles, remove them and try again to check if everything is fine.
All the best,
the Telerik team
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