The difference which is often lost on non-civil-law-countries people is the split between copyright itself (i.e., the fact I am the author, right to avoid my work in dishonesting way, and some other bits) and my right to economically exploit my work (e.g., ask for royalties). These two are separable in the civil law countries, and although the former cannot be transferred and assigned ever, the latter can be, and actually it expressly is by the created-on-job provisions (if you create the work as part of fulfilling your obligations from the employment, your employer is the automatic assignee of the economic rights to such work).
However, I don’t think in the end, this distinction is that important, and it can be covered mostly by the salvator clause (“If any portion of this section is held invalid or unenforceable …”).