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.