WPF custom command in context menu are disabled until any button clicked

I have a custom command and I try to execute them from the context menu, but they are always displayed as disabled unless I click any button on the UI (buttons do not have anything to do with commands).

After clicking a button, commands start to be displayed correctly (when they are unavailable they get disabled and enabled if available).

Edit: it turns out that it is not the button click which makes command work correctly, but button or other controls in focus (e.g. if I tab into a control this also enables my commands).

Here is the code for commands:

<Window.InputBindings>
    <KeyBinding Command="{x:Static local:MainWindow.Quit}" Key="Q" Modifiers="Ctrl"/>
    <KeyBinding Command="{x:Static local:MainWindow.Disconnect}" Key="D" Modifiers="Ctrl"/>
</Window.InputBindings>

<Window.ContextMenu>
    <ContextMenu Opacity="95">
        <MenuItem Header="Quit Application                  Ctrl + Q"   Command="{x:Static local:MainWindow.Quit}"/>
        <MenuItem Header="Disconnect from the pump   Ctrl + D" Command="{x:Static local:MainWindow.Disconnect}"/>
    </ContextMenu>
</Window.ContextMenu>

Here is the commands CanExecuteMethod:

public static RoutedCommand Quit = new RoutedCommand();   

private void QuitCanExecute(object sender, CanExecuteRoutedEventArgs e)
     {
      e.CanExecute = true;
      e.Handled = true;
     }