I'm not seeing that problem on kfreebsd-i386, at least?Interesting. I got the above output on asdfasdf.debian.net's unstable chroot (kfreebsd-amd64, AFAIK).
The key difference might be exact python version. Inside sid chroot: python2.6 2.6.7-4 python2.7 2.7.2-11 asdfasdf:~$ CFLAGS='obscure' python2.6 x.py CFLAGS='-fno-strict-aliasing -g -O2 -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes' asdfasdf:~$ CFLAGS='obscure' python2.7 x.py No CFLAGS variable asdfasdf:~$ python2.6 x.py CFLAGS='-fno-strict-aliasing -g -O2 -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes' asdfasdf:~$ python2.7 x.py Empty CFLAGS Petr