解释是当你点击一个ButtonBase时，控件会捕获鼠标。这意味着所有鼠标输入事件都使用ButtonBase作为源，即使鼠标输入事件是在元素边界之外触发的。
解决方案是在公共父容器上侦听路由的鼠标输入事件，并使用CaptureMode.SubTree控制鼠标捕获。
您可以通过访问RoutedEventArgs.Source属性来标识感兴趣的事件源：

<Grid PreviewMouseMove="Grid_PreviewMouseMove">
  <Grid.ColumnDefinitions>
    <ColumnDefinition />
    <ColumnDefinition />
  </Grid.ColumnDefinitions>

  <Button Grid.Column="0"
          Background="Red" />
  <Grid x:Name="BlueGrid" 
        Grid.Column="1"
        Background="Blue" />
</Grid>

private void Grid_PreviewMouseMove(object sender, MouseEventArgs e)
{
  // Capture mouse for the complete sub tree instead for a single element.
  // In this case this includes the Button and the Grid.
  // Because messing with the mouse capture could potentially break 
  // the ButtonBase.Click event and ButtonBase.Command handling 
  // you may have to fallback to use the UIElement.PreviewMouseLeftButtonUp event 
  // to execute the Button.
  _ = Mouse.Capture(this, CaptureMode.SubTree);

  // Filter the event source to handle BlueGrid mouse move events
  if (e.Source is Grid grid 
    && grid.Name.Equals("BlueGrid", StringComparison.OrdinalIgnoreCase))
  {
    // TODO::Handle mouse move over BlueGrid
  }

  // Relasae mouse capture
  _ = Mouse.Capture(null);
}