Some of these shares may represent shares contracted to institutions which haven't been delivered yet. But the fact that the underwriters had to enter the market at all is an ominous sign. If shares decline below $38, not only will these institutions miss out on the big dollars they were counting on, this could turn into a serious loser for them. These are long stock positions, there is no hedge.
Morgan Stanley, the lead underwriter is not very big in the RIFIN, but JP Morgan and Goldman Sachs are big components.
Watch FB share price for guidance regarding FAZ/FAS on Monday.