The described behavior is not common. You could take a look at the demo below which filters numbers correctly and it is bound programatically client-side. You could debug what values are passed to the method which filters the grid and observe if they are correct in order to try and resolve your issue. If your problem still persists you could provide us with the page declaration and the associated code behind so we could investigate further and advise you with the best possible solution.
the Telerik team
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