Juniper made investors happy with yesterday's third-quarter earnings, but one of the question marks hovering over the company is its tepid outlook for gross margins.

Analysts aren't buying Juniper's explanation for muted gross margins of 62.9 percent last quarter. A bit of uncertainty isn't unusual, but some reactions are bordering on suspicion.

"We’re still struggling to square the company’s recent gross margin softness with their comments about the fundamental sources of that softness," writes Jeffries analyst George Notter in a note issued this morning.

What's troubling analysts is that Juniper's gross margins were higher than 64 percent for most of last year. There was some hope that recovery would be in sight, but Juniper CFO Ken Miller said on yesterday's call that 63 percent was a more "prudent" prediction "not only for Q4 but in the near term."

Reasons Juniper cited for the 62.9 percent figure included the mix of products sold and the mix of customers who were buying last quarter. (Juniper sells primarily to service providers but has worked on increasing its business with cloud providers.) But some analysts don't think that adds up.

"The mix [of products sold] should have helped gross margin this quarter," writes analyst Simon Leopold of Raymond James in a note published this morning.

Notter's guess, based on experience, is that there's a wrench in the works, one item that's pushing down on gross margins in general. His hunch is that it's the new QFX 10000 product line.

"We’re guessing Juniper is pricing their new QFX10000 series data center switches aggressively in order to win market share with specific cloud provider customers. Our guess is that Juniper may be trading lower profitability for higher revenue growth among larger content provider customers," he writes.

That's pure speculation, of course, but it's not a bad guess, and it certainly wouldn't be the first time a company cut some deals in order to seed the market for a new product. The QFX10000 plays a starring role among the products Juniper announced last year. It's a data center spine switch that Juniper claims is going gangbusters, with sales up 50 percent from the third quarter last year.

Juniper declined to comment, citing a policy not to comment on Wall Street research.