Christopher Nolan might be starting to wonder if somebody has it in for him. First The Dark Knight director is cruelly ignored by the Golden Globes, despite his superhero sequel being one of the best-reviewed films of the year. Then his name starts disappearing off copies of the film distributed to Oscar voters.

When members of the Academy of Motion Picture Arts and Sciences and other awards bodies received their shiny new Dark Knight DVDs through the post this week, many noticed that something was missing. The words "A Christopher Nolan film" had been scrubbed out - somewhat amateurishly - with black felt-tip pen.

According to Defamer, the mysterious censorship is down to a longstanding dispute between writers and directors over the use of the "possessory credit". The Writers Guild of America (WGA) claims that the formulation "a film by [director's name]" is offensive to its members because it ignores their contribution to the movie-making process.

According to the Hollywood Reporter, the writers looked to have won the battle in 1963 when WGA negotiators persuaded the Alliance of Motion Picture and Television Producers to agree that no one could use the term unless they at least wrote the film in question. The Directors Guild of America (DGA) would not let that lie and in 1967 launched a historic lawsuit against the WGA for credit control. However, things were settled out of court three years later when Lew Wasserman, the all-powerful head of MCA, laid down the law that in return for the writers agreeing not to drag the matter into collective bargaining - thus heading off a potential strike - the studios would limit the instances of these credits.

The agreement failed to hold and the credits proliferated. And even though the DGA in 2004 agreed a voluntary code limiting the use of the possessory credit to established film-makers, the issue remains a bone of contention.

A spokeswoman for Warner Bros confirmed to Defamer that the apparent censorship of Nolan's name stemmed from the WGA's longstanding position. "It's because the guild won't accept a possessory credit for a director," she said.

Whether the move makes any difference to Nolan's chances of a best director Oscar nomination may be a moot point. The British film-maker has so far failed to win plaudits from any of the critics' bodies whose awards are seen as early indicators of Oscar success. None the less, the late Heath Ledger, who gave a career-defining performance as the Joker in The Dark Knight, has been nominated for a Golden Globe for best supporting actor in a drama and received the best supporting actor gong from the Los Angeles Film Critics Association.