iRobot reported strong backlog growth for its defense and security business. Photo source: iRobot Corporation.

iRobot (NASDAQ:IRBT) just announced reasonably solid second-quarter results -- but the market sure isn't happy. The stock was down nearly 9% in early afternoon trading.

On one hand, iRobot's quarterly net income rose slightly year over year to $8.5 million, or $0.28 per share, which easily beat Wall Street's expectations for earnings of $0.22 per share. Keep in mind, however, that the company's second-quarter results were also skewed by a $0.07 per-share benefit from the release of a tax valuation allowance relating to its acquisition of Evolution Robotics. Adjusting for that item, iRobot's earnings per share would have come in a penny below the consensus estimate.

iRobot's Roomba vacuums continue to sell well. Photo source: iRobot

In addition, while iRobot's quarterly revenue rose 7.2% year over year to $139.8 million -- which was within the company's previous guidance range -- it fell slightly short of analysts' expectation for sales of $142.5 million. And this despite continued strength in iRobot's crucial home robot business, for which management raised the low end of its full-year revenue expectations by $5 million to $505 million.

Here's what's holding iRobot back -- for now
If you're wondering why the market is in a tizzy, look no further than iRobot's government-centric defense and security business. Though D&S expects "several near-term orders" and saw "strong backlog growth during the quarter," increased visibility for the segment caused iRobot to lower 2014 revenue expectations for the segment by $5 million to $45 million. iRobot CEO Colin Angle explained, "The increased visibility has clarified that certain order deliveries are being requested by the customers for early 2015 [...]." Translation? Over the long term, these orders are still expected to arrive.

For now, though, iRobot lowered both the top and bottom ends of its overall 2014 revenue expectations by $5 million to a new range of $555 million to $565 million. At the same time, iRobot curiously raised its 2014 earnings per share guidance from $1 to $1.15 to a new range of $1.10 to $1.20. Analysts, on average, were modeling lower full-year earnings of $1.11 per share on higher sales of $564.8 million.

So why the discrepancy? When asked during the earnings conference call to clarify the guidance, iRobot CFO Alison Dean explained that management had already anticipated the tax increase -- which strictly impacts EPS and not revenue -- to arrive in the back half of this year. With this in mind, iRobot built in downside protection in its guidance in the event the tax benefit didn't arrive. So when it unexpectedly hit the books ahead of schedule, the result was iRobot's seemingly contradictory guidance adjustments.

Foolish takeaway
So what does that mean for investors now? First, iRobot stock isn't terribly cheap, trading around 42 and 25 times trailing and forward earnings, respectively. So it's not surprising that shares pulled back today given the top-line shortfall.

But to be honest, I think today's drop is a huge overreaction to what effectively comes down to a meager $5 million in delayed -- not lost, mind you -- orders for iRobot's already-small defense and security business. Considering that the backlog for D&S is robust, and that iRobot's core home robot business is still going strong, I'm convinced patient, long-term investors have no reason to sell their iRobot shares today.