> I'd imagine that bug is reproducible with `Path('C:\\Temp', 'C:')` 
> already, right? If that's the case, should it logged as a 
> separate issue?

Yes, it's a separate issue that affects the _from_parts() call in absolute().

How about designing absolute() to create a new instance from an absolute path that's created by os.path? For example: 

    join(abspath(self.drive) if self.drive else getcwd(), self)

Of course use accessor functions.