Reversed Channels

Several examples have been cited over time where songs come out on a CD, etc. with the channels reversed over the original. I don't understand how that happens. I realize the engineer who is mastering the track has many options and opinions as to EQ, etc., but having the channels right seems pretty basic and I don't see how that can get goofed up. Any insights would be appreciated.

 

I don't have any insight, but I have a Henry Mancini CD that features highlights from four of his soundtracks (60's)...there is some odd channel switching going on there! Odd, like instruments that have swapped places with left and center! I'd have to listen to it more closely later, but I think on this CD, the two-channel may have been remixed from original master tapes. Not sure though.

 

Here is a bit more info.
http://www.stevehoffman.tv/forums/showthread.php?s=&threadid=6757