Lawrence Yun NETAR via Vimeo Earlier this morning, the National Association of Realtors told us that existing home sales fell 1.5 percent in September to 4.75 million. This was right in line with expectations.

However, median home prices jumped by 11.0 percent year-over-year.

Here's what NAR chief economist Lawrence Yun had to say about that: "The shrinkage in housing supply is supporting ongoing price growth, a pattern that could accelerate unless home builders robustly ramp up production."

This speaks to a troubling dynamic that's been developing in the market for new homes.

In recent months, homebuilders have been ramping up the construction of new homes. In a new report from the Census, housing starts surged to a their highest levels since 2008.

The problem is that new home sales haven't been keeping up pace. Here's a chart from TD Securities economist Millan Mulraine:

Meanwhile, homebuilders like Lennar and PulteGroup, who are both bullish on housing, will be under immense pressure by shareholders to keep building.

The September new home sales report will be coming out next Wednesday. This is one report the housing economists will be keeping a very close eye on.

SEE ALSO: FORGET ALL THE HOUSING COMEBACK TALK: Here's Why The Market Is Still A Disaster >