Putting special characters in the title should have no adverse effect on the layout or functionality. Special characters in the post title have been known to cause issues with JavaScript when it is minified, especially in the admin when editing the post itself (ie. issues with metaboxes, media upload, etc.).

Verify that: The post title renders the word « with » in italics and the word « markup » in bold. The post title markup should be removed from the browser window / tab.