StatusBar binding a value was not displayed

[sawanhai]

Describe the bug

i try to binding status ,and when keydown change status value. but OnHotKey method and propertyChanged event was not display status value to window;

Steps to reproduce

clone code, and edit MahApps.Metro demo; MainWindowViewModel.cs

private async Task OnHotKey(object sender ,HotKeyEventArgs e){ 
       this NumericUpDownValue =2;
}

MainWindow.xaml

<StatusBar Grid.Row ="2">
     <StatusBarItem>number value</StatusBarItem>
     <StatusBarItme Content="{Binding NumericUpDownValue,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" />
</StatusBar>

build and run ,keydown hotKey ;default ctrl+shift+home;

Expected behavior

StatusBar should show number value :2 ;

Actual behavior

StatusBar doesn't change;

Environment

MahApps.Metro version: v2.4.9 Windows build number: Win10 Visual Studio: 2019 16.8.3 Target Framework: .Net 4.5.2

Screenshots