I've owned a lot of frustrating stocks in my life, and Jamba Juice parent Jamba (NASDAQ:JMBA) is starting to climb up there. The company announced preliminary second-quarter results yesterday, and they're as lumpy as a Jamba Juice smoothie during a power outage.

Really.

Jamba grew its top line by 14% to $89.6 million during the second quarter. That is better than the 9% advance that Wall Street has been expecting, but don't look for growth at the store level. Comps fell by 3.3%.

Expansion is driving the burst. The company tacked on 27 new company-owned store locations during the period. It watches more than 645 stores total, with plans to open 90 company-owned stores this year. It is looking for franchisees to open another 30 units, less than the 50 franchised locations it once figured would pop up in 2007. I hope the franchisees aren't getting cold feet over the store-level decline or Jamba's own inability to turn a consistent profit.

The company blames the same-store weakness, in part, on California weather. It's an odd crutch, given that West Coast chains like Jack in the Box (NYSE:JBX), California Pizza Kitchen (NASDAQ:CPKI), and Chipotle (NYSE:CMG) all posted great comps this past quarter. Sure, there are different dynamics behind ducking in for a refreshing smoothie fix and grabbing a full meal, but why is Jamba Juice struggling?

From Starbucks to bucking stars
A few months ago, I was proclaiming Jamba to be the Starbucks (NASDAQ:SBUX) of juice bars. I've been inside a half-dozen locations, and they all ooze with feel-good energy boosts. As with Starbucks, patrons are passionate about the product. They never flinch as they pay more for a beverage than they would for a combo meal at a fast-food joint down the road.

Maybe it's just me, but I always seem to walk into Jamba Juice stores that are a whirlwind of activity. The feverish tapping of a blender being emptied into a tall polystyrene cup keeps the beat going long after I've left the store.

I realize that not every smoothie on the menu is good for you, but at least I feel good about what I'm consuming. Besides, the company has been beefing up its collection of healthy slurps. Its latest line of functional smoothie products offers nutrients and antioxidants that tackle everything from fat to cholesterol. If Coca-Cola (NYSE:KO) is moving in that direction with vitamin-stoked drinks and metabolism enhancers, it's good to see Jamba ahead of the curved bottle.

Unfortunately, the fundamentals aren't following suit. It seems as if every few weeks, Jamba is creeping lower into the single digits. If the trend continues, you'll be able to exchange a single share certificate for a 16-ounce smoothie.

Right place, right time, wrong stock
It's sad, but true. Jamba should be in a much better place right now. It has seasoned leadership. It's got a former Burger King (NYSE:BKC) president as its CEO. Its chairman served as Wayne Huizenga's right-hand man. It has a great concept that practically runs itself as a license to print money. It shouldn't be hog-tied to weather conditions in any single market given its success in new markets.

The rub is that it's not printing money. That blender tapping I keep hearing? It's actually the sound of me and my fellow investors getting hammered. Jamba won't be reporting the rest of its fiscal second-quarter numbers until the end of the month, but I'm not all that upbeat, given the troubling comps.

I'm not going to bail on the company, and that's why owning it has been so frustrating. I'm a realist. I understand that profitability is going to be erratic as the company builds out its company-owned store empire. That doesn't come cheap. Still, why is it that Chipotle -- another fast-growing chain with a similar base of self-owned locations -- is hitting the cover off the ball every quarter?

Why isn't a company charging better than $5 for a cup of blended fruit rolling in more dough than a California Pizza Kitchen kitchen? The company has had a few quarters under ballyhooed leadership, so it's not as if shareholders haven't been patient.

So I'll keep holding, slurping, and lying to myself. Maybe there's a functional smoothie in there that can jog my memory or buck me up for the coming earnings report. 

Chipotle was recommended in both Motley Fool Hidden Gems (B Shares) and Rule Breakers six months ago. Coca-Cola is an Inside Value recommendation. Forget functional smoothies for a moment. Feed your brain (and perhaps your wallet) with a free 30-day trial subscription to any of the Fool's newsletters.

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Longtime Fool contributor Rick Munarriz is about a 10-minute walk from a Jamba Juice, and he makes that trek often. He does own shares in Jamba. He is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. The Fool has a disclosure policy, and it comes with a free immunity boost.