Assignment, rights in a recording and in an underlying work: a need for explanation

Peter Lawton, of London-based Cacophony Ltd write to ask for a bit of guidance. He says:

"I am a music publisher and have been trying to explain the difference between the copyright in the recording and the copyright in the underlying composition to a Polish company. They claim the law is different in Poland and when an artist signs a record contract they automatically assign the composition as well. They use the phrases "economic rights" and "derivative rights" (note: not defined and meaningless to me in this specific regard) to substantiate their claim.

I've been digging around to find something specific but reasonably intelligible to someone who's English is less than perfect (but an awful lot better than my Polish) which explains in either English or Polish -- with English translation so I can check it -- that the two rights are not the same and that EU legislation distinguishes between the two. I thought it would be easy to find but it seems not.

If anyone feels in the mood to give me bonus I also need to explain that covering a song does not mean the copyright in the composition is automatically acquired by the performer as well.

Responses, anyone?