This happens to me whenever I travel now. Every time I've called to check on this, the agent just tells me that I am on the waitlist and basically they are holding these seats to see if there is a possibility that they could sell them before they allow you to claim them...so much for those 72...24 hour windows for upgrades.
Another thing you may want to check is to see how full/empty coach is...if it looks like coach is already oversold, then it is guaranteed that they are waiting to see if they can sell these FC seats before giving them away for free.