One mystery resolved. >From django/core/management/commands/loaddata.py line 297:
elif fixture_name == 'initial_data' and fixture_files: warnings.warn( 'initial_data fixtures are deprecated. Use data migrations instead.', RemovedInDjango19Warning ) Under python2, the fixture_name contains u'initial_data', so the if condition fails. Under python3, the fixture_name contains 'initial_data', so the if condition succeeds. This is no doubt because the tests/fixtures/tests.py file contains "from __future__ import unicode_literals" at the very top. Still not sure why this only recently became an issue in unstable. -- Brian May <br...@microcomaustralia.com.au>