Which has code according to your example.
When I cancel out it closes the window but when I open window second time and click on cancel it closes current window and now it's showing the old window again. For this example I am using radWINModalPostLogin windwow.
<
telerik:RadWindowManager ID="radWindowManager" Style="z-index: 8001;"
runat="server" Skin="Vista" OnClientClose="OnClientClose" EnableViewState="false" ShowContentDuringLoad="false" >
<Windows>
<telerik:RadWindow ID="radWINModalPostLogin" runat="server" ReloadOnShow="True" DestroyOnClose="true" Behaviors="None"
Left="" VisibleTitlebar="False" VisibleOnPageLoad="false" Style="display: none;" Top="" Modal="True" KeepInScreenBounds="True" >
</telerik:RadWindow>
<telerik:RadWindow ID="radWINDialogPostLogin" VisibleStatusbar="false" runat="server" VisibleOnPageLoad="false"
Left="" VisibleTitlebar="True" Style="display: none;" Top="" Modal="False" Behaviors="Close" >
</telerik:RadWindow>
</Windows>
</telerik:RadWindowManager>