Likutey Tefilotes 19. Emphasizes the need to read the Targum in order to make the distinction of the text. Why would the work of an illustrious convert be the tree of life and the work of our master, Moshe be only the tree of knowledge?
The Shabbas with it's blessing and it's curse applies only to the slaves of G-d. Someone who is proud and does Shabbas, is only fooling himself and others, he is not really a student of Rabenu (rather of Amalek). The convert on the other hand became a slave of his own free will, so his Shabbas IS Shabbas.