Something is overriding my comments= commands

I have a .vimrc where I run:
set comments=

I added the command to my ~/.vim/cpp.vim file and ~/.gvimrc file as well. Yet somehow, I have comments set to a non-blank value that puts garbage all over my files when I run my comment creation macros. I can unset it by hand in every session, but the point of the .vimrc file is to avoid doing that every time.

Is there a way to see where this is getting set? Or to somehow turn it off system-wide (short of a custom compilation)?

Here's my vim --version:
VIM - Vi IMproved 7.3 (2010 Aug 15, compiled Oct 26 2012 16:45:33)
Included patches: 1-547
Modified by pkg-vim-maintainers@lists.alioth.debian.org
Compiled by buildd@
Huge version with GTK2 GUI. Features included (+) or not (-):
+arabic +autocmd +balloon_eval +browse ++builtin_terms +byte_offset +cindent
+clientserver +clipboard +cmdline_compl +cmdline_hist +cmdline_info +comments
+conceal +cryptv +cscope +cursorbind +cursorshape +dialog_con_gui +diff
+digraphs +dnd -ebcdic +emacs_tags +eval +ex_extra +extra_search +farsi
+file_in_path +find_in_path +float +folding -footer +fork() +gettext
-hangul_input +iconv +insert_expand +jumplist +keymap +langmap +libcall
+linebreak +lispindent +listcmds +localmap +lua +menu +mksession +modify_fname
+mouse +mouseshape +mouse_dec +mouse_gpm -mouse_jsbterm +mouse_netterm
-mouse_sysmouse +mouse_xterm +mouse_urxvt +multi_byte +multi_lang -mzscheme
+netbeans_intg +path_extra +perl +persistent_undo +postscript +printer +profile
+python -python3 +quickfix +reltime +rightleft +ruby +scrollbind +signs
+smartindent -sniff +startuptime +statusline -sun_workshop +syntax +tag_binary
+tag_old_static -tag_any_white +tcl +terminfo +termresponse +textobjects +title
+toolbar +user_commands +vertsplit +virtualedit +visual +visualextra +viminfo
+vreplace +wildignore +wildmenu +windows +writebackup +X11 -xfontset +xim
+xsmp_interact +xterm_clipboard -xterm_save
system vimrc file: "$VIM/vimrc"
user vimrc file: "$HOME/.vimrc"
user exrc file: "$HOME/.exrc"
system gvimrc file: "$VIM/gvimrc"
user gvimrc file: "$HOME/.gvimrc"
system menu file: "$VIMRUNTIME/menu.vim"
fall-back for $VIM: "/usr/share/vim"
Compilation: gcc-4.6 -c -I. -Iproto -DHAVE_CONFIG_H -DFEAT_GUI_GTK -pthread -I/usr/include/gtk-2.0 -I/usr/lib/x86_64-linux-gnu/gtk-2.0/include -I/usr/include/atk-1.0 -I/usr/include/cairo -I/usr/include/gdk-pixbuf-2.0 -I/usr/include/pango-1.0 -I/usr/include/gio-unix-2.0/ -I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include -I/usr/include/pixman-1 -I/usr/include/freetype2 -I/usr/include/libpng12 -g -O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat -Werror=format-security -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1 -I/usr/include/tcl8.5 -D_REENTRANT=1 -D_THREAD_SAFE=1 -D_LARGEFILE64_SOURCE=1
Linking: gcc-4.6 -L. -Wl,-Bsymbolic-functions -Wl,-z,relro -rdynamic -Wl,-export-dynamic -Wl,-E -Wl,-Bsymbolic-functions -Wl,-z,relro -Wl,--as-needed -o vim -lgtk-x11-2.0 -lgdk-x11-2.0 -latk-1.0 -lgio-2.0 -lpangoft2-1.0 -lpangocairo-1.0 -lgdk_pixbuf-2.0 -lcairo -lpango-1.0 -lfreetype -lfontconfig -lgobject-2.0 -lglib-2.0 -lSM -lICE -lXpm -lXt -lX11 -lXdmcp -lSM -lICE -lm -ltinfo -lnsl -lselinux -lacl -lattr -lgpm -ldl -L/usr/lib -llua5.1 -Wl,-E -fstack-protector -L/usr/local/lib -L/usr/lib/perl/5.14/CORE -lperl -ldl -lm -lpthread -lcrypt -L/usr/lib/python2.7/config -lpython2.7 -lpthread -ldl -lutil -lm -Xlinker -export-dynamic -Wl,-O1 -Wl,-Bsymbolic-functions -L/usr/lib -ltcl8.5 -ldl -lpthread -lieee -lm -lruby-1.9.1 -lpthread -lrt -ldl -lcrypt -lm -L/usr/lib

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