I am not able to reproduce the described issue. Could you please explain in more details your scenario? Based on your screenshots, I assume that you are using the SpreadSheet component within a Window. In which browsers, do you reproduce the issue? Do you reproduce it in our basic demo site: Filtering or without the Window?
If it will be convenient for you, you could send us a sample dojo.telerik.com where we would be able to examine the behavior.
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