Hi Michael Chong,
You can use the Closed event and PreviewClosed event to achieve what you are willing to. If you hook up on the PreviewClosed event and set the Cancel property of WindowPreviewClosedEventArgs to true, the Closed event will not be invoked.
The latest official build is the one you use, we provide internal builds every Friday that include fixes and new small changes to the official version. If you have any other questions feel free to contact us.
the Telerik team