It was beyond obvious:
“Facebook’s underwriters had to step in to support the company’s share price, people familiar with the matter said. In particular, lead underwriter Morgan Stanley MS -0.82% was assigned to be the deal’s “stabilization agent”—meaning it was the firm’s job to keep the shares above the offering price, these people said. In that role, Morgan Stanley was forced to buy Facebook shares as the price slid toward $38 in order to prevent the price from crossing into negative territory, according to these people.”
MSCO would only have been expected to buy a set amount of facebook before letting it crack 38 (who knows how much, an awful lot obviously).
The things I thought of here are 1) this was a HUGE offering, hundreds of millions of shares and 2) more retail got allocations than any IPO I Have ever heard of, which is in itself a contrarian indicator.