Something we have talked (and joked) about for years has been the blatant plagiarism from Kenji Yamamoto in various bits of music for the franchise. Some pieces have taken inspiration, but others have been flat-out "stolen" — examples such as Cell's theme from Super Butôden 2 on the Super Famicom (Pink Floyd's "One of These Days") and "Battle Point Unlimited" from DBZ TV Episode 120 (Propaganda's "The Murder of Love", among other of their songs) come to mind.
From its inception, there have been allegations from fans about Yamamoto's score for DragonBall Kai, his first foray into solely scoring a TV adaptation of the series (previously only having composed and arranged additional vocal songs while Shunsuke Kikuchi handled BGM composition for the DragonBall and DragonBall Z TV series, as well as scoring various video games).
Toei has finally acknowledged this practice, specifically with regard to DragonBall Kai. In an official statement posted on their website yesterday, Toei noted:
The existence of multiple suspicious musical pieces which may infringe on the rights of third parties has been confirmed within the musical compositions recorded for "Dragon Ball Kai", an animated television work produced by this firm. The relevant musical pieces are used as background music in "Dragon Ball Kai", and measures are promptly being taken to replace the relevant musical pieces from the background music of "Dragon Ball Kai".
Also, we are proceeding with a swift investigation of the facts, and discussion of countermeasures with concerned parties in the near future.
The culprits are likely BGM tracks named "The Ebb and The Flow" and "A New Foe Rears His Head" which are essentially the tracks "War" by James Horner from the Avatar score and the Terminator Salvation opening theme by Danny Elfman, respectively. Both of these pieces were included on DragonBall Kai Soundtrack III & Songs and are used in the series beginning in the "Jinzôningen & Cell arc" around the time that Trunks appears (coincidentally, just about where the television broadcast of the English dub happens to be these days). Keep in mind that Toei themselves have not actually named specific pieces of music, so while this is not quite "speculation" or "rumor", it should be held in check.
This would seemingly explain why the fourth soundtrack collection for the "refreshed" TV series was canceled for a second time.
Toei's official website for DragonBall Kai (as well as Fuji TV's own site) now solely list Shunsuke Kikuchi as staff under "Music."