The inadvertent disclosure of an investigation by the Public Company Accounting Oversight Board into Deloitte & Touche’s 2003 audit of truck maker Navistar International Corp. raised eyebrows recently as the first formal probe of a Big Four firm by the Board. But the probe should be of interest to public companies for another reason: It raises an important issue regarding the disclosure of PCAOB investigations by auditors to their public company clients.

News of the Board’s investigation surfaced in a Bloomberg report earlier this month, after the Securities and Exchange Commission—which oversees the PCAOB—inadvertently disclosed the probe when a confidential document ended up in a public file.