But not anymore, because as Deutsche Bank's chief international economist notes in a Wednesday note, the historical relationship between stocks and bonds is breaking apart, prompting Slok to exclaim that "something is wrong", as it could portend danger for those investors holding Treasurys in the hope these would cushion the slide in stocks.

it is no secret that bond prices and stocks are inversely correlated, or at least have been in normal times, but all that changed this year as Treasury prices have largely failed to reflect the slump in stocks, as MarketWatch notes.

"What is safe to say is that there is something driving equities lower, which is not impacting rates. Or there is something keeping long rates high, which is not impacting equities," Slok wrote in a Wednesday note.

This correlation breakdown has undercut the bond market's status as a safe haven in a year in which few asset classes have eked out positive returns. This correlation "failure" was on full display yesterday when despite the record point surge in the Dow, Treasury yields posted a very modest move higher (one which has since been faded on Thursday). And, as MW notes, if traditional havens like U.S. government paper struggle to shield portfolios from a further selloff in equities it could mean investors will lack few reliable boltholes going forward.