Another reason demand for the long bond has been so voracious is that a lot of investment banks still use them to hedge their corporate-bond positions and interest-rate swaps (between fixed- and floating-rate obligations).

ECONOMIST: Bond bombshell

For one thing, it is hard to know how much companies have in fact lengthened the maturity of their debts because the interest-rate swap market allows them to swap those fixed bond payments into cheaper floating debt, a popular strategy in the investment-grade market.

ECONOMIST: Better to feast on cookies than junk bonds