The same example can be constructed for python3 by modifying the imports.

I think what is happening here is that if a has not yet been imported, then when 'from .a import test' is done, the import machinery loads a and then defines 'a' in the local namespace, overriding the previous 'import package.b as a'.  On the other hand, if a has already been imported, the import machinery finds 'a' in sys.modules and skips the import-and-set-name-in-local-namespace step.

IMO the bug is that 'a' gets set at all when 'from a import test' is done, but the fact that it does so has a long history.