Are you sure that a 'partially frozen package' is the reason for this? And not that CPython has one module set its __name__ to another module's name for some backward compatibility purposes? More precisely: _collections_abc.__name__ is set to collections.abc.
I'm not 100% sure, but I know a bit about Python's import system, and I think this is the problem. import collections.abc will find the frozen collections package, and not carry on to look in the zip file. I also confirmed that in the example you gave, the library.zip file does contain collections/abc.pyc.
I don't think the __name__ of _collections_abc is actually relevant here, though I imagine it could cause other weird effects.