Apple is reportedly investing a bug in iTunes Match that replaces music containing explicit lyrics with "clean" versions from the iTunes Store. Cult of Mac had this to say about the bug:
iTunes Match had successfully filtered out all the profane and derogatory words by changing the tracks to clean versions of the albums, which pretty much ruined my jog because I was really really wanting to sing along and drop 50 “F-bombs” a minute. Maybe this is just a rare glitch in iTunes Match’s system, but it’s a travesty tantamount to treason in my eyes and I want it fixed.
9to5 Mac now says Apple has acknowledged the problem, but hasn't come up with a fix just yet.
A 9to5 reader emailed Apple Senior Vice President of Internet Software and Services about the issue a couple of weeks ago and received a response from one of Eddy Cue’s engineers. According to the engineer, Apple is currently investigating the issue and working on a fix. Apple has no interim workaround for users of the iTunes Match service, the email elaborated.
So don't be surprised the next time you fire up some 50 Cent only to find that all the swear words have been removed. Apple is aware of the issue and is working towards a resolution. In the meantime, you'll just have to go about your rap-listening sessions in censored manner.