An error atypical of Lata Mangeshkar? Or some recording issue?

“Kambakht galti se bhi besura nahi gaati (She doesn’t sing out of tune even by mistake),” who doesn't know this immortal comment of admiration of Bade Ghulam Ali, the Ghazal maestro, on Lata Mangeshkar, the nightingale of India? Come the opportune moment, perhaps, any music lover of the sub-continent would love to allude to these words of eulogy for the epitome of musical infallibility.

Of course, she was the parable of virtues in terms of her moving about the ambit of music and its application into reality just for the sake of her longing for relishing aesthetic pleasure. But this inquisitive reference to one very rare moment in the span of her entire mellifluous vocation may leave one to decide whether it was really something unbecoming of the legend, or an irrectifiable technical glitch while recording the song?

The 1983 film Bade Dil Wala (https://en.wikipedia.org/wiki/Bade_Dil_Wala) had some superhit numbers sung by Kishore Kumar, Lata Mangeshkar, Udit Narayan and Baby Preeti. Quite sure, any moment, one might start humming to the tunes of 'Aaj Kahin Mat Jaa' or 'Jeevan Ke Din'. Such is the music composed by R. D. Burman upon the lyrics of Majrooh Sultanpuri!

But these two are not the ones about to be brought under the scanner. It is the Lata-Kishore 'gipsy' duet 'Kaho Kaise Rasta Bhul Pade' (https://youtu.be/dvMtPok85y8). The song picturized on Rishi Kapur and Aruna Irani has three antaras (https://www.lyricsmotion.com/song/lyrics/kaho-kaise-raasta-bhool-gaye). The second antara begins:

“Raste ruk jaate hai, jab kaate boti hai,

Jane-ja tum kya jano dunia kya hoti hai…”

Just when Kishore Kumar sings the word ‘Jane-ja’, another voice, or something that seems to be a voice, streams in unexpectedly, as if on a wrong footing, pressing upon the word of Kishore Kumar. On minute scrutiny, one may trace out the half-articulated syllable, sounding like ‘Hu/(m)' [at 02.32/33 of the above YouTube video]. Another thing to notice is that even Aruna Irani appears to have opened up her mouth in a manner as if to utter something. So, maybe it was a pre-decided anomaly suggested by the team associated with the song just to make a difference, to add the flavour of variety that should look natural on screen. 

Most interestingly, when the third antara begins with Kishore Kumar singing: 

"Banjare kiske yaar, aisa sab kahte hai..."

Lata Mangesh replies with: 

"Hum jiske ho jate hai, uske hi rahte hai..."

So, if not an error on the part of the legendary singer, it must have been some technical issue with the recording of the song. 

But in the end, we rest assured that whatever it be, it does not in any way diminish the charm of listening to this evergreen Lata-Kishore duet.