Updated from 3:52 p.m. EDTTwo months after its $585 million IPO blew out of the gates, Refco ( RFX), the big derivatives brokerage, finds itself embroiled in a painful accounting scandal involving its chief executive. New York-based Refco said Monday that CEO Phil Bennett took a leave of absence after the company determined it was carrying a $430 million receivable from him without labeling it as a related-party transaction. A Bennett-controlled company ran up the debt by buying a package of hard-to-collect receivables owed to Refco by unrelated third parties. The good news for Refco is that Bennett, an obviously wealthy man who pocketed more than $118 million in the firm's initial public offering, paid back the $430 million plus interest on Monday. The bad news is that the scandal mauled Refco's shares and left them trading below their $22 offering price for the first time since the Aug. 10 IPO. The stock closed down $12.96, or 45%, to $15.60. As recently as Oct. 3, the stock was above $30 a share. A regulatory source says the Securities and Exchange Commission, which is close to sanctioning the firm in a separate matter involving its role in a private stock placement, will probably look into the latest scandal. One thing regulators could focus on is whether Bennett deliberately hid his role at the company that bought the Refco debt in order to ensure that the IPO went forward. If Bennett's interest in the entity or the poor quality of the underlying receivables were fully disclosed to investors, it's possible the IPO might have priced at a lower valuation. Refco's IPO was led by Credit Suisse First Boston, Goldman Sachs and Bank of America. A spokeswoman for CSFB declined to comment. Sources say the underwriters, who are charged with doing their own due diligence before bringing a deal public, only recently learned of the accounting problems.