There’s been a ton of coverage about the Facebook IPO disaster, but very little of it looks at the crucial point two weeks ago where things went terribly wrong. It’s becoming increasingly clear that Facebook itself messed up at that juncture.

The screw-up resulted in a major disappointment in Facebook’s stock debut: The stock’s 15 percent decline since the IPO last Friday may not in itself be tragic. But worse, lawsuits are flying saying that legal guidelines weren’t followed. And there’s the sad fact that regular mom-and-pop investors were apparently left with the more losses on average than large institutions who got privileged information. This all was aggravated by a separate annoyance: glitches in the Nasdaq stock market trading process, which caused delays in trade and cancel confirmations, among other things.

However, based on a number of interviews VentureBeat has had with observers and other sources close to the process, it’s apparent that Facebook itself may be most to blame for the fallout. Facebook chose to be more furtive in public announcements about its business than it was in private talks with large investors.

The decisive action by Facebook came on May 9, three days into the “roadshow,” which is the time when Facebook and its bankers visit major investors in hopes of getting them to buy the IPO stock. On that day, Facebook’s executives, led by chief financial officer David Ebersman, signed off on new language in the company’s updated IPO prospectus.

In that May 9 update, Ebersman decided to use vague language when describing how the company’s second quarter was looking. According to the filing, specifically on page 57, Facebook said that it was experiencing the same trend in the second quarter that it had seen in the first quarter, that growth in “daily active users” (DAUs) was increasing more rapidly than the growth in ad impressions, driven by many users’ shift to mobile devices.

The exact wording is here:

Now Facebook is generally growing quickly — and its ads are growing, even if they are growing more slowly on mobile — and so this update itself didn’t send any alarm bells to most investors, and it shouldn’t have. After all, Facebook had long warned about this mobile problem, ever since the first IPO prospectus filing on Feb 1, that revenues could be negatively affected by its huge mobile growth, because monetizing mobile hadn’t been proven. (Indeed, VentureBeat was the first to report this on the day of the IPO filing.)

Facebook’s lawyers may, in the wake of the legal mess it has gotten into, try to argue that the new May 9 language about “DAU’s increasing more rapidly than the increase in number of ads delivered” pointed to something more significant than Facebook had released before. But the reality is that this wording was just too vague to be construed by normal people as meaning anything more than what had already been mentioned before. The sad things is, this was such an important update for Facebook, its team must argued about it a hundred times before publishing. So why was it written as though it was purposefully trying to obfuscate? More on that in a sec.