This is reproducible with RadMaskedNumericInput and RadMaskedCurrencyInput, when the Mask property is empty.
UpdateValueEvent is LostFocus. FormtString is non default - for example n2 or c2.
When all text is selected and delete key is pressed, the Text will become "$,." or "-." or "($)" - non digit symbols remain in text.
Expected: Text becomes empty string "".