为MenuItem使用DataTemplate会导致左侧出现额外的空间？

Whenever I attach a DataTemplate to a MenuItem, each generated menu item gets an extra space on the left side. This extra space looks as wide as the space reserved for the check, which I use. Building a menu manually without a DataTemplate doesn't add this extra space. As an extra wrinkle, if I click on this extra space the menu item goes away but no click event is generated. I don't know why it's adding this extra space. Any ideas?Whenever I attach a DataTemplate to a MenuItem,