Baked Alaskan: Is that the "Walnut Theme"? From the Stephanie's comments in the User comments there, I believe version 1.7.0 does not exhibit that behaviour.
Maybe you should update it? Try Tools/Add-ons, select Themes and click "Find Updates"
(Cacher) Gardez votre boîte au lettres propre en Archivant les messages importants et en utilisant régulièrement l'option Effacer Tous Les Messages. (pauloaguia) (Montrer toutes les astuces)