In this story about Peter Jackson suing New Line Cinema for underpaying him for his work on The Lord of The Rings trilogy (wherein the central part of the complaint is that New Line / Warner Brothers sold off rights to the spin-off materials to its subsidiary companies at lower-than-market value):

But Mr. Socarides said some lucrative rights did not go to Time Warner companies. The pay television deal went to Starz, not Time Warner's HBO. He added that the "Rings" book trilogy remains with Houghton Mifflin, which is not a Time Warner subsidiary.

Because obviously, New Line had the right to sell those rights on…I'm sure the Tolkien estate might have had a few words about that…