It looks like there might be a contradiction in the documentation of import in the language reference. In the loading subsection https://docs.python.org/dev/reference/import.html#loading, first bulleted list of the section, it specifies that if a loader fails, it must remove only the failing module from sys.modules, while other side-effect imports by loader will stay in sys.modules.

In the next subsection https://docs.python.org/dev/reference/import.html#loaders, second bulleted list (last bullet), the phrasing is confusing, and possibly contradictory. I believe that it meant to reiterate what was said above (see my previous paragraph).

Attached is a potential patch, but if anyone finds that I am interpreting this wrong, I'll make adjustments accordingly.