Mishnah Berurah

1. The Sefer Mishnah Berurah was a joint effort of the Chafetz Chaim, his son-in-law, and his son, hence there are a number of contradictions that crept into the Sefer. The Chazon Ish reportedly did not think this was the case: the Chafetz Chaim most certainly reviewed the Sefer thoroughly to make sure there were no contradictions.
2. Rav Asher Weiss notes how the Mishnah Berurah is subtle but novel in his approaches to Halacha and often disagrees with the Shulchan Aruch and Rama. Rav Hershel Schachter points out that he got away with it but "כאשר עשה כן יעשו לו!"