This is not an error of duplication. The full-fledged version of this Mitzvah are many and change for those who are learning the one/three chapter a day.
Negative Mitzvah 252
It is forbidden to hurt a convert's feelings
Exodus 22:20 "You shall not wrong a stranger"
A "Ger" is a person who converted to Judaism and took upon him-or herself to keep the Torah and Mitzvot.
We are commanded not to hurt his feelings or say anything that may cause the Ger to be embarrassed or feel uneasy.