Praise then darkness, and creation unfinished

When I went to sync my iPod a little while ago, I got an error message saying that the computer was no longer authorized for this iPod, and would I like to authorize it. I said yes, and gave it my password, and it put it through and told me that I had now authorized four of the five allowable computers. A few months ago, the same thing, with "three."

Clearly, this is not going to end well. I believe, from checking this last time, that I can tell it I am deauthorizing some of these nonexistent or overlapping machines (I think my dead PC is one of them). But does anyone know how to prevent this, or why it's happening? All the Apple pages I found last time were just "here's the fix/workaround" with no ideas of why it was happening.