I am referring here to US Immigration, not TSA.

Have any US Citizens on this forum experienced this before for no appearant reason (or was not told why)?

I've read a number of stories on the internet that if this happened once, this will happen almost every time you travel back to the US ...

If it happened once and the additional inspection has found nothing why wouldn't US Immigration straighten the record so that they would not create more inconvenience to the traveller as well as themselves in the future?