iRobot Corporation (NASDAQ:IRBT) just released reasonably solid fourth-quarter results. But if iRobot stock's 8% after-hours drop is any indication, the market isn't happy. So what happened?

On one hand, quarterly revenue climbed 20.7% year over year to $159.3 million. That's within iRobot's guidance range, but below Wall Street's optimistic expectations for sales of $164 million. Net income, on the other hand, nearly tripled to $0.31 per share, which is both at the high end of iRobot's expected range and above analysts' expectations for earnings of $0.30 per share.

"All three of our businesses met our expectations and made significant progress against their strategic plans," said iRobot CEO Colin Angle, "setting us up well for 2015."

iRobot enjoyed solid 19% year-over-year growth in overall Home iRobot sales, including an increase of over 20% domestically and 17% overseas. Meanwhile, though iRobot's press release didn't contain specifics, it did say the Remote Presence business "continued to ramp sales" of RP-VITA telemedicine robots for use in hospitals, and it sold Ava 500 Video Collaboration robots to "several" Fortune 500 companies.

Finally, iRobot says its Defense & Security business "delivered results consistent with expectations, exited 2014 with a solid backlog, and is positioned for healthy growth in 2015." For perspective, this means iRobot's D&S business is poised for its first year-over-year sales increase since 2011.

On guidance
Speaking of which, for the current quarter iRobot expects revenue of $114 million to $117 million, and earnings per share of $0.08 to $0.10. Both ranges are well below analysts' expectations for sales and earnings of $133.8 million and $0.27 per share, respectively.

To its credit, iRobot's full-year outlook at least partially narrows that gap; iRobot expects 2015 revenue of $625 to $635 million, representing 12% to 14% growth over 2014, and earnings per share between $1.25 and $1.45. Even so, the midpoint of both ranges sits below analysts' expectations for 2015 revenue and earnings of $643.1 million and $1.44 per share, respectively.

Unfortunately -- and despite the return to growth in Defense & Security -- iRobot expects Home Robot revenue to still represent 90% of 2015 revenue as growth decelerates to a range of 11% to 13%. Angle explained though it expects Home Robot sales in the U.S. to enjoy continued momentum with growth in the mid-teens, international sales "will be tempered by macros and currency devaluations."

Next, iRobot's Remote Presence business will focus primarily on improving the scalability of its solutions, while holding revenue relatively flat on a year-over-year basis at just $3 million.

Teasing new products
We should also keep in mind that iRobot has demonstrated a knack for favoring caution, typically underpromising and overdelivering on its full-year guidance. There's no guarantee it's doing the same this time around. But as I noted on Tuesday, you might recall that iRobot stock initially plunged in after-hours trading after last year's fourth-quarter report, when the company provided weaker-than-expected 2014 guidance, only to pop more than 12% the following day, after management offered its encouraging perspective for the future during that morning's conference call.

Incidentally, Angle offered one such tantalizing hint at what's to come in iRobot's press release today, saying, "2015 will be an important year for iRobot as we begin to roll out and monetize investments we have been making in crucial robotic technology."

iRobot CFO Alison Dean also recently gave new perspective on how the company is investing for the future, detailing tens of millions of dollars spent each year on not just improving its existing moneymakers, but also advancing key technologies such as low-cost manipulation, video navigation, and even leveraging the cloud for resource intensive tasks such as object detection, large map storage, and communication between devices.

Naturally, I'll be listening closely to iRobot's Thursday morning conference call to see whether management is willing to elaborate on Angle's comment. But as it stands, I'm simply not convinced that iRobot's report today is as bad as the market seems to indicate.