On The Beatles' first LP, Please Please Me, the songs were credited to McCartney/Lennon, but for every subsequent album they were always Lennon/McCartney. Paul McCartney, however, recently (2002) released a live album "Back In The US" containing many Beatles songs, curiously credited to "McCartney/Lennon." Mayhem ensued.
Macca claims that the original agreement was that
if we ever wanted it could be changed around to make me equal, and that he wants to make it clear which songs were written by whom. He apparently decided the latter after seeing a music book which credited "Hey Jude" to John Lennon, when in fact the song was almost entirely Paul's.
Paul McCartney's place in history is probably pretty well cemented. Whether this manipulation of the credits is justified or just self-indulgent is up to you. In any case, Yoko Ono, John's widow, is planning to sue if she can, having turned down Paul's request for permission to reverse the credits for "Yesterday," another Beatles song that was primarily McCartney's, on the Beatles Anthology 2. Whatever ends up happening, it's doubtful that it will help the Beatles' reputation for getting along.
Source: Garcia, Gilbert. "The Ballad of Paul and Yoko." http://www.salon.com/ent/music/feature/2003/01/27/paul_yoko/index1.html.
Also my dad, for bringing this to my attention.