What: Shares of Demandware (NYSE: DWRE) were down 11% as of 11:45 a.m. after the enterprise cloud commerce solutions specialist released stronger-than-expected third-quarter results, but followed with disappointing subscription revenue guidance.

So what: Quarterly revenue rose 49% year over year to $57.6 million, including a 39% increase (47% on a constant currency basis) in subscription revenue to $47.8 million, and an 80.6% increase in revenue from the services and other segment to $7.0 million. Demandware's number of live customers also climbed 27% year over year to 308, while live sites increased 36% to 1,399.

Based on generally accepted accounting principles, that translated to a net loss of $11.9 million, or $0.33 per share, compared to a GAAP net loss of $0.18 per share in the same year-ago period. On an adjusted basis -- which means excluding things like stock-based compensation and acquisition costs -- Demandware achieved net income of $2.6 million, or $0.07 per share, up from non-GAAP net income of $0.03 per share in last year's third quarter.

Analysts, on average, were anticipating an adjusted loss of $0.09 per share on lower revenue of $53.5 million.

However, Demandware also reduced its guidance for 2015 subscription revenue to a range of $199 million to $201 million, down from prior subscription revenue guidance of $200 million to $205 million. To its credit, however, thanks to strength in services, Demandware also increased the bottom end of its previous overall 2015 revenue guidance range by $3 million, resulting in a new range of $233 million to $235 million.  Wall Street's consensus estimates called for total 2015 revenue at the low end of this range.

Now what: While the market's reaction to what otherwise seemed a strong report might seem strange, investors are right to be concerned by what seems to be decelerating growth from Demandware's core subscription revenue. During the subsequent conference call, management elaborated that guidance was driven by lower-than-expected volumes beginning in Q2 from "a small group of specialty apparel customers," which continued into the third quarter.

What's more, "overage" fees -- that is, when newer customers often exceed their minimum commitment based on higher-than-expected sales through Demandware's platform -- declined on a year-over-year basis for the first time in Q3, so guidance appears to project a further decline in overages in Q4. To be fair, this is a somewhat natural consequence as longer-term customers get a better grasp of their volumes and increase their minimum commitments to avoid overages.

Nonetheless, while Demandware is certainly still growing at a healthy pace, investors want to know it can sustain growth in subscriptions where it matters most in these early stages. With shares trading at over 200 times next year's estimated earnings and nearly 11 times trailing-12-month sales, I can't blame investors for taking a step back today.