Copied from Zylar's post:

Bill Bolin, ex-song writer for Homestuck, wrote original music for flash pages, including the Midnight Crew flash and Jade: Retrieve Package.

One day Hussie needed songs for this page and used multiple works that Bolin posted on the music team forums. Bolin called those works unfinished and unrepresentative of his abilities as an musical artist, and as such was upset that Andrew used them in their unfinished state in an update. He asked Andrew why he posted his material without his consent. Andrew claims he didn't know the music was unfinished, but was satisfied with their quality enough to both canonically place them in the story and release it in a Homestuck music album.

Bill was distraught over Andrew's behavior. Bill also held some grudges with other members of the music team and disliked the format Andrew used to direct the music. As Bill expressed his grievances, the general reaction among the team was that he was overreacting, his music was one of the most used at the time, and that he would make good money on it. Bill's rant eventually spilled out into the general MSPA forums with a thread of his posting a picture of him giving the middle finger. Controversy and confusion in the forums followed.

Andrew had originally decided to take out only the unfinished work from that one page on the flash, but after the post and controversy he opted to completely cut ties. All the flash pages that previously used Bill's work were given new music, and all of them were removed from the Homestuck albums.