Reason for being non-free: modified files must be renamed and clearly identified. Why is this in non-free?
Steve Langasek: "ISTR this license element came up for discussion in the context of the LaTeX license; I /thought/ the conclusion was that requiring changes to filenames in the source was ok, but that requiring changes to filenames in the binary package was not" (discussion) Elsewhere, Knuth says that "Public-domain sources for all programs and data of The Stanford GraphBase are freely available."
Branden Robinson: "I don't believe that's correct. A requirement to change the filename at any stage was dropped from the latest draft of the LPPL that Frank Mittelbach posted to debian-legal (summer 2003).
I personally would maintain that a requirement to change a filename is an unacceptable restriction on one's freedom to modify the work. The LaTeX Project no longer appears to be interested in contending this issue, and I know of no other copyright holder of software packaged by the Debian Project who does." (discussion)