No, I've always been in Multiple Window mode, which doesn't seem to jive with what you deduced.  I was still in Multiple Window mode when I resized the whole Item List window to just less than full screen, then resized the columns and they stayed.  I'd never done that before.  And Like I said, now the resizing works even in One Window mode!  That shouldn't be the case if your theory is true.  So I'd say you're onto something with your theory, but it's not quite working the way you think.