My take is iTunes using the date/time added to maintain the tune sequence within an album. At lest that is the only criteria I can find that iTunes might use to retain the sequence within an album.
On the one hand, maybe, but on the other, wouldn't it be intuitive, make more sense, and even be easier to program if visible columns were considered as user preferences and iTunes simply sorted from left to right rather than by some arcane algorithm?
I could then have "Date Added" as my third column and see what I want intuitively rather than have it mysteriously introduced into my mix.
It seems to me to be pretty unApple-like behavior. (I wonder if it persists in later versions of iTunes than my v 8.2.1.)
And I find this curious, although it may not be: If your scenario is on the mark it would mean that invisible (Date Added) data is being accessed while, at the same time, iTunes "Search" can't access info in an invisible (Comments) column.