When all Splitter's RadPanes have height configured in pixels, the control cannot be resized with the browser even if its width is set to 100%.

Steps to reproduce:
1. Run the following code and try to resize the width of the browser:
        <telerik:RadSplitter ID="VisualSplitter" runat="server" Orientation="Horizontal" Height="600px" Width="100%">
            <telerik:RadPane ID="TNPane" runat="server" Height="200" BackColor="WhiteSmoke" ContentUrl="Grid.aspx">
            </telerik:RadPane>
            <telerik:RadPane ID="ICPane" runat="server" Height="400" Scrolling="None" BackColor="Red" >
            </telerik:RadPane>
        </telerik:RadSplitter>


Temporary workaround:
Set the sum of all RadPanes' height as height of the Splitter and remain one RadPane's height not configured (the Splitter will calculate it on its own):
        <telerik:RadSplitter ID="VisualSplitter" runat="server" Orientation="Horizontal" _Height="600px" Width="100%">
            <telerik:RadPane ID="TNPane" runat="server" Height="200" BackColor="WhiteSmoke" ContentUrl="Grid.aspx">
            </telerik:RadPane>
            <telerik:RadPane ID="ICPane" runat="server" Scrolling="None" BackColor="Red" >
            </telerik:RadPane>
        </telerik:RadSplitter>