How to debug this import problem?

[Iwan]

Mmm, we solved half of the cause of this one.

Test runs are kicked off via setuptools's test command. But this
happens programmatically, and successively in one process.  But
setuptools's test command clears all modules imported during a test
run from sys.modules - hence it is intended that modules would be re-
imported.

Why certain of our code managed to still get to the classes contained
in prior imports is still a mystery though.

-Iwan