Hello Gong,
Thank you for your question.
We will need some time to investigate this behavior. As soon as we have more information on that matter we will contact you again. Please excuse us for any inconvenience caused.
In the mean time as a workaround you can inherit the RadMaskedTextInput and override its HandlePaste() method.
In this case you will need to remove the binding for the default PasteCommand, otherwise the HandlePaste() method will be called twice. You can do it with the following code snippet:
For your convenience I prepared a sample project demonstrating this approach. Please give it a try and let me know if it helps. Also, note that this is a custom implementation that is not well tested and doesn't check for all border cases, this is why I recommend you to test it before use it in your code.
Regards,
Martin
Telerik
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