Hi Jegan Raj,
Thanks for the workaround, I had tried the PreviewKeyDown event but its not raised for some reason and I didn't think of trying the PreviewKeyDown event instead. Anyways, I refactored your code into an Attached Behaviour which is set in the implicit style that targets DateTimeEdit, it is set to Enabled when the property IsEmptyDateEnabled is itself set to true via a style trigger. It works great. Nonetheless I think this behaviour should be wired in the control itself, in a future release perhaps!
Here's my code: