Price growth has exceeded rent growth in national indexes for single-family homes, according to CoreLogic chief economist Frank Nothaft. But what would ordinarily be a signal of trouble has been offset by a couple of factors. However, there's no guarantee how long that might continue.

"Home prices rose a whopping 20% over the past year and rents on single-family homes were up 13%, according to the CoreLogic national Home Price Index and Single-Family Rent Index," Nothaft wrote. With the disparity, he raised the question of whether that might mean homes are overvalued.

The math is simple on the surface, as he noted. The price of a rental home should be equal to the net operating income divided by the capitalization rate. Prices have been going up because investors essentially are trying to buy into ongoing growth of net operating income through the growth of rents.