Americans' take-home pay is rising but only modestly, a trend that continues to confound economists.

July's jobs report affirmed the stasis, showing that average hourly earnings rose 2.5% from a year ago, and in line with the average seen since the start of 2016.

Bank of America Merrill Lynch's economists frame the issue in terms of economic theory that expects a tighter labor market will eventually force employers to pay workers more:

"The fact that the unemployment rate continues to slide without acceleration in wages remains a puzzle.

This could reflect a variety of factors including low productivity growth, employee insecurity about the health of the labor market, skill mismatch and sector specific stories.These factors likely will continue to be in play, but we think that it is only a matter of time before there is a modest move higher in wage growth. The bigger uncertainty is whether or not this translates to consumer price inflation."

And here's Michael Shaoul, chairman and CEO of Marketfield Asset Management:

"There is no obvious weakening of overall wage increases in recent months, but equally no sign that overall wage growth is starting to accelerate.

Although the FOMC would clearly be more comfortable with wages growing faster we do not view the current situation as a meaningful barrier to further policy tightening."