Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of infrastructure specialist MasTec (NYSE: MTZ) were getting disassembled by investors today, falling as much as 28% in intraday trading after the company reported third-quarter results.

So what: There was some good news in MasTec's third-quarter report. Earnings per share edged up from last year to $0.36, matching analysts' estimates. The company's backlog also looked particularly strong, finishing the quarter at $3.1 billion, the highest ever and up 35% from last year.

However, that the $0.36 in earnings per share came on a big beat on the revenue line meant that the company's margins took a big hit during the quarter. Management blamed the drop in profitability on wet weather in the Marcellus Shale and a tough time meeting its primary wireless customer's (aka AT&T (NYSE: T)) "aggressive build plan."

Now what: In truth, the current quarter didn't look all that bad. The problem was that management was very upfront about the fact that the two major issues above would extend into the fourth quarter and would affect the quarter's results. Investors haven't taken kindly to this. And to be sure, it doesn't sound good that volume is expected to be down from AT&T -- a customer that accounted for 20% of the company's business in 2010.

Of course, it's very possible that investors are overreacting to the expected softness in the upcoming quarter. The company's backlog and the strong third-quarter revenue suggest that MasTec is doing something right. And when looking out to 2012, CEO Jose Mas described his outlook as "excellent."

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Fool contributor Matt Koppenheffer owns shares of AT&T, but does not have a financial interest in any of the other companies mentioned. You can check out what Matt is keeping an eye on by visiting his CAPS portfolio, or you can follow Matt on Twitter, @KoppTheFool, or on Facebook. The Fool's disclosure policy prefers dividends over a sharp stick in the eye.