I can't reproduce this: in bzr.dev:
bzr diff -r -500 bzrlib/tests/test_diff.py and bzr diff -r -500 bzrlib/selftest/testdiff.py produce the same results.
I can't reproduce this: in bzr.dev:
bzr diff -r -500 bzrlib/ tests/test_ diff.py and bzr diff -r -500 bzrlib/ selftest/ testdiff. py produce the same results.