From a recent article of mine, this is what I was asked, and how I responded:
Okay, 30-year swap yields have been less than Treasuries for some time. I’m not totally certain as to why. There are a lot of games going on in the derivatives markets, and they seem to favor buying long and financing short. I do know that there are gains to be made in the short run from taking the opposite position, unusual as that is… but as with any anomaly in the market, be cautious, because the motives of other players shift, making opportunities more attractive, less attractive, or unattractive.