Core template update strips

I am making changes to the core templates under Design/Templates and the default templates that you created have html values in before/after of some tags, such as {excerpt before=”<div class=’mc-excerpt’>” after=”</div>”}

When I want to add my classes (or even just pasting the example above) they are stripped when saving the template: {excerpt before=”<div>” after=”</div>”}

Do you know why this could be and how to fix it?
Huge thanks