Are there traditions in Shia books such as Bihar Al Anwar that suggest that the Quran is distorted? If so, how can their presence in those books be explained?
Quran is intact with out any distortion whatsoever. There are narrations in Sunni books like Bukhari, Muslim, Al-Tirmithi, Al-Nasaa'ee, Ibn Maajah, Muwatta' Malik, Musnad Ibn Hanbal and other well known books claiming stories about distortion in some Suras of Quran. Our authentic evidence that Quran is intact, made our leading Ulama reject any narration contradicts with the fact that Quran is intact even if it the narration is mentioned in a Shia book. Such narrations in Shia books are much less than in Sunni books and some of them were copied from Sunni books. Such narrations are either fabricated or misunderstood.
Bukhari in Hadeeth number 4608 narrated from Umar ibn al-Khattab different words in Quran which never recited by the Prophet Muhammad (SAWA). Bukhari narrated in Hadeeth number 6327 and 6328 from Umar ibn al-Khattab a claimed verse on stoning the old man and old woman. Such verse is not in Quran but Umar said it is. These are just few examples of long list of such rejected Sunni narrations on this matter.
'The fact which we believe in according to most authentic evidence from Ahlul Bayt (AS) is: Quran is intact and preserved and protected by Allah (SWT) from distortion.
Wassalam.