MaskedTextBox - the mask is not working correctly

[nikulenko]

Avalonia 12.1.0.

Mask 0 - Digit, required. This element will accept any single digit between 0 and 9.
There should not be a space inside a group of numbers - this is a control behavior error.
The problem occurs when a bound property attempts to convert the contents of a string to a number.

<StackPanel VerticalAlignment="Center" Margin="20">
    <MaskedTextBox Mask="0000" />
</StackPanel>