It seems that there is some compatible problem using RadTextBox control with the VIE Telex keyboard
But, if you set explicitly the Text in the ViewModel, to string.Empty, it seems that the content is successfully cleared. The problem if you are using the "clear button" of the RadTextBox control is still present, so you can just collapse it by setting the ClearButtonVisibility property to "Collapsed".
Please find attached a sample project demonstrating clearing the text of the RadTextBox control and don't hesitate to contact us again if this approach is not applicable for you.
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