What I am seeing is a sprite image from the old Telerik MVC Extensions. It is complelety unclear what styles cause it to appear in the described scenario - I guess there is some custom CSS code that you are using. Please inspect the Tooltip and its contents with a DOM inspector to find out more information about the applied styles and where they come from. For example, you may need to disable background image repeat, or use a single icon for a background image, instead of a sprite image (if the element that has the background image applies is large by design).
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