For those lacking long memories, Apple and Nokia were embroiled in a bitter patent dispute from 2009 to 2011, with both companies filing a series of legal complaints and regulatory challenges as competition in the smartphone market came to a head.

The issue was ultimately settled in June 2011, and while terms of the agreement were kept confidential, Apple was expected to make amends with a one-time payment and ongoing royalties.

Now it appears that Judge William M. Conley of the US District Court for the Western District of Wisconsin owned shares in Apple at the time of the case.

The court clerk Joel Turner said that Judge Conley informed him about the conflict of interest and that  his ownership of stock neither affected nor impacted his decisions in this case.

It is unclear how many shares Judge Conley possessed during the case, but ownership of company stock in any capacity would have required his recusal under the Code of Conduct for United States Judges. An advisory from the Judicial Conference Codes of Conduct Committee explains that disqualifying factors should be reported "as soon as those facts are learned", even if the realisation occurs after a judge issues a decision.

"The parties may then determine what relief they may seek and a court (without the disqualified judge) will decide the legal consequence, if any, arising from the participation of the disqualified judge in the entered decision", Advisory Opinion 71 reads, as relayed by Turner.

Apple and Nokia are invited to respond to Conley's disclosure by Oct. 27 should they wish to seek redress, though the companies are unlikely to take action considering the case was not a linchpin in Nokia's overarching strategy.