I actually had the same question and asked some backers, and apparently there was a backer-exclusive post about it.
Here is it:
https://www.kickstarter.com/project...me-3d-collect-a-thon-platformer/posts/1210802
At the start of composing the 3rd track, Grant had raised some concerns about his style of music fitting in with the rest of the game. Seeing as Grant is a veteran composer, we did not take his concern lightly and after discussing the situation we both reached a mutual agreement for him to stop at this point. He pointed out that there were no bad feelings over this decision and he felt Pascal could carry on doing a great job. We don't want anyone to feel any sort of hard feelings towards Grant, as he has done an outstanding job, and we fully respect this decision.
So there was no drama at all, just Grant deciding to limit his participation due to his style not being quirky enough for the game.