Hi Emmanuel:
By default the Tweet button sharing will take content of the element of your page, which in this case includes literal text that you you’ve also used for microdata. The element should not contain other elements, and there’s no way for us to detect if the code there is intentional or accidental.
To fix it: Either ensure that your CMS does not include other content in the page title, or you can set the text parameter of the share link explicitly, to not include your extra mark-up.
Ben