Checkbox tick direction

I have a checkbox as per the photo below. I'm curious why my 'checked' symbol look so weird and laterally inverted. I intentionally to use FlowDirection ="RightToLeft" is to ensure my text is at left side of the checkbox.

Below are my XMAL:

<CheckBox Grid.Column="1" Grid.Row="9" Content="Stop Immediately"
          IsChecked="{Binding StopImmediately}" FlowDirection="RightToLeft"
          Margin="-30,15,5,0" />