RadNumericUpDown does not fire propertychanged when empty

Hi,

I encountered an issue with the RadNumericUpDown control. I have defined the UpdateValueEvent to PropertyChanged, this works fine as long as I am entering valid numeric values. But in case that I just delete the whole text from the NumericUpDown control the value is not updated in my viewmodel because the setter for the binded value is not called. When I leave the RadNumericUpDown afterwards the setter is called correctly and the value in my viewmodel is set to null.

This is my definition in XAML

<telerik:RadNumericUpDown Value="{Binding DurationFrom, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
                ValueFormat="Numeric" NumberDecimalDigits="0" ShowButtons="True"
                Minimum="1" Maximum="{Binding DurationTo, Mode=OneWay, TargetNullValue=1.0}"
                NullValue="" UpdateValueEvent="PropertyChanged" />

Is this a known issue with the NumericUpDown control and is there any workaround for this?

Regards,

Micha