space bar(single click) not working in the textbox which is in content template

[Gowd]

   

 In the splitbutton control.i have below issues. xaml code is below for that.

<telerik:RadSplitButton.ContentTemplate>

<DataTemplate>

<telerik:RadWatermarkTextBox/>

</DataTemplate>

</telerik:RadSplitButton.ContentTemplate>

in the radawatermarktextbox which is located in the datatemplate->content template the space bar is not functioning properly.
when I click on space bar its not effecting in the  text.if I hold the spacebar then its starting moving.

please help me out on this.