is about to pull off its best first half of a year in at least 10 years and the Dow Jones Industrial Average is having its best June since 1938, but underneath this impressive rally is a trend that doesn't seem quite right, according to J.P. Morgan.

From consumer discretionary to technology, cyclical stocks that typically are tied to economic growth have failed to regain the ground lost in May, whereas only defensive groups like consumer staples and utilities have confirmed the S&P 500's new highs, J.P. Morgan's chart analyst Jason Hunter pointed out.

"Rally leadership doesn't inspire a lot of confidence yet ... In our view, that cross-market divergence can only persist for a short period of time, and the S&P 500 Index rally potential is limited under the current conditions," Hunter said in a note on Wednesday.

Indeed, the market's strong comeback in June has little to do with economic fundamentals. It's largely driven by the shift in Federal Reserve's monetary policy and the revived hopes for a trade deal between the U.S. and China. The persistent weakness in cyclicals stocks that traditionally correlate to economic health could be especially worrisome as the corporate profit picture continues to deteriorate.