Just because a bug appears seemingly randomly does not mean it's not a bug.
When I was a kid watching tv with an indoor antenna, anytime there was poor reception I'd go and hold the antenna and reception would improve or get a lot worse.
So, I've no problems believing that this is an issue, that it affects different people differently at different times, and that Apple knew about it and made those shells as a fix (a trade-off in exchange for greater compactness of the device) for those who want it.