It means that IP that was developed in the US becomes owned in a tax haven so that the profits from such IP are not taxed in the US. This is why companies find it profitable to put jobs overseas even if there is no business reason to do so.
I am really intrigued by Rashkin's comment. You write: Rashkin told Congress that the current structure encourages U.S. companies to “park the resulting intellectual property in tax havens.”
What does that mean?