My complete configuration is this:

[loggers]
keys = app_admin,root,app_test_py3
[logger_root]
handlers = ""
[formatters]
keys = app_admin,app_test_py3
[handlers]
keys = app_admin,app_test_py3
[logger_app_admin]
propagate = 1
handlers = app_admin
qualname = nagare.application.admin
level = INFO
[handler_app_admin]
formatter = app_admin
class = StreamHandler
args = (sys.stderr,)
[formatter_app_admin]
format = %(asctime)s - %(name)s - %(levelname)s - %(message)s
[logger_app_test_py3]
propagate = 1
handlers = app_test_py3
qualname = nagare.application.test_py3
level = INFO
[formatter_app_test_py3]
format = %(asctime)s - %(name)s - %(levelname)s - %(message)s
[handler_app_test_py3]
formatter = app_test_py3
class = StreamHandler
args = (sys.stderr,)

I wanted to provided a non-working configuration as small as possible, that was accepted by python 2.7.

It seems you are right there is a problem with this configuration as it shuts down logging in python 2.7. It looks like i have a bug in my configuration generation.

By the way the patch restores python 2.7 behavior as expected, thanks.