While it is no secret that Fannie Mae is facing a capital shortfall in the wake of an unfavorable accounting ruling by the Securities and Exchange Commission, it is unclear exactly what prompted the GSE’s regulator to declare the company “significantly undercapitalized” for regulatory purposes. According to the Office of Federal Housing Enterprise Oversight, Fannie held $38.03 billion in core capital and $38.76 billion in total capital as of Sept. 30. This put the GSE…