I am afraid that this is not a supported scenario and you need to remove the function which you have assign to DateSelected client even from the document.ready. Generally this function will be executed when a date is selected and if you need to fire it when the control is loaded you can use the OnLoad event. Please check out the following code snippet.
<telerik:RadDatePicker ID="datePicker" runat="server" MinDate="1900-01-01"
DateInput-Width="217px" Culture="en-GB" Calendar-ClientEvents-OnLoad="OnLoad"
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