Did commodity indices break the wheat market?

The Senate's newly published Levin-Coburn report thinks so. CME has promptly "refuted" the charges. Felix Salmon buys it (and makes the connection to the USO oil ETF's exacerbation of oil contango).

It's very complicated to prove anything in this arena - my hunch is that the indices did play a large part in non-convergence of wheat contracts at the least, and maybe higher volatility as well, but I haven't seen anyone prove it to my own satisfaction.