The reason for it? The way Zune recognizes tags and the way iTunes recognizes tags are two entirely different formats. The issue itself actually lies in the Zune software, as I recall, as when I was using Zune (back while having a Zune 120gb) I had everything tagged and properly ordered via Zune, but when I loaded up MP3s in anything else, a lot of the information was missing (particularly with Winamp).