Sharafudin Musawi says:
"Although we are convinced that no distortion has taken place in the verses of the Noble Qur'an and that our heavenly Book has not been tampered with in any way, it is by no means clear that the arrangement and recension of the verses is precisely that in which they were revealed.
For it is quite possible that the 'purification verse' concerning the People of the House was revealed separately and then, when the verses of the Qur'an were being assembled, was placed in the middle of the verses relating to the wives of the Prophet, either in error or deliberately." (Sharaf al-Din al-Musawi,
Kalimat al-Ghurra', p.213.)
Link from major Shia website:
http://www.al-islam.org/imamate-and-leadership-sayyid-mujtaba-musavi-lari/lesson-19-confirmation-quran-and-sunnah Other link:
http://www.imamreza.net/eng/imamreza.php?id=1036&page=7Opinion of
Majlisi:
فلعل آية التطهير أيضا وضعوها في موضع زعموا أنها تناسبه ، أو أدخلوها في سياق مخاطبة الزوجات لبعض مصالحهم الدنيوية
ولو سلم عدم التغيير في الترتيب فنقول : سيأتي أخبار مستفيضة بأنه سقط من القرآن آيات كثيره ، فلعله سقط مما قبل الآية وما بعدها آيات لو ثبتت لم يفت الربط الظاهري بينها
“It is possible that the purification verse was added (by the Companions) at this part (of the verse) claiming that it was referring to the wives, or they added in the verses addressing the prophet’s wives, to suit their religious needs…Even if we accept that there was no tampering (by the Companions) in the order (of the verses), we say there are many narrations which discuss the removal/canceling of Quranic verses. [Maybe there were verses before and after the verse of purification and they were removed]; if these verses were not removed before and after the verse (of purification), we would see the apparent link between them.”
(source: Bihar al-Anwar, vol.35, pp.234-235)