Multicam sequence out of sync BUT nest source sequence perfectly in sync - BUG?

[zeebra10]

Premiere Pro 15.1

I've been multicam editing for a while now, I understand 'audio drift'. This is different, in the middle of my multicam edit, all 4 cameras get out of sync with the audio. Go to my nested source sequence to see what is going on... everything is in sync, audio and 4 cameras. Go back to my multicam sequence... audio waveforms are in sync for each camera with the main audio BUT video is out of sync with audio. 

Shouldn't the nested sequence also show this out-of-sync issue? 

[Bertrand27675085f1z3]

Wish this had a fix... I am having the same problem over a year later