Isn't this just a case of failed QC specs?

I don't know the first thing about yoga or yoga pants, but this is a terribly interesting problem: too-sheer yoga pants. From the New York Times:

Even novice shoppers know to wiggle around in a pair of pants before you buy them. But that was a lesson that Lululemon Athletica overlooked when it stocked too-sheer yoga pants, leading to a product recall, an expected hit of around $60 million in lost sales, and the risk that Lululemon — a widely envied retailer — has at last given competitors an opening. 

The company is recalling yoga pants made with a fabric known as Luon that are overly transparent, which make up about 17 percent of all the Canada-based retailer’s women’s bottoms. 

Lululemon’s chief executive, Christine Day, said Thursday that the company did not know exactly why the quality had gone awry, as the pants had passed quality-assurance tests. But she added that “the truth of the matter is that the only way that you can actually test for the issue is to put the pants on and bend over,” which the company did not do until too late.

From the Wall Street Journal, more details on the specific problem from Ms. Day:

"The only way that you can actually test for the issue is to put the pants on and bend over," she said on the call. "It wasn't until we got into the store and started putting it on people that we could actually see the issue." 

As for quality control, "We've had a standard metric-based system ... for a very long time that controls it within the environment at the manufacturer," Ms. Day said. But there are "a couple of gaps that we found" that are harder to measure and really are more subjective," she said. "And that's certainly one area that we feel that we can do a better job of controlling.... We have to do a better job of controlling or creating standards for that process as we're shipping to more locations to manufacture."

If the material is too thin (or is see-through when stretched), isn't this an easily solved QC problem? I would think you could weigh the fabric (or the pants) or you could stretch out randomly selected batches of cloth to see if you could see through them. Mannequins, maybe? Surely Ms. Day is not suggesting that she has to hire people to actually try on every single pair of yoga pants.

What I find most interesting about this issue, from a manufacturing standpoint, is that people are speculating that this happened because they started to work with new suppliers and scale up their production. I'm glad to know sudden, out-of-nowhere specification surprises don't just happen when scaling up chemical manufacturing.