The disparity we observe between the credit and stock markets can be explained by too much money in the system and momentum-trading computer algorithms.
Some of the money being placed into the financial system by the central banks eventually finds its way to the stock markets. The markets are now driven by machines, which find trends and exploit them. A little extra money raises stock prices. The machines note this and buy into the momentum which causes other machines to join in and so on.
In the thin August markets, this effect is exaggerated.
I am aware that this scenario begs the question, “What happens when liquidity disappears and the process begins to work in reverse?”