It would appear that Harmonix isn't the only Activision partner who has is in a legal tiff with the publisher. Guitar manufacturer Gibson, whose guitar body styles are licensed for Guitar Hero controllers, says Activision is infringing on a nine year old patent for technology to simulate a musical performance. Reuters reports that Activision has in turn filed suit in federal court to render that patent claim invalid.
According to the report, Gibson sent Activision a letter in January requesting that the Guitar Hero pub apply for a license or stop selling the game. Activision essentially responded, "We thought since you didn't say anything about it, we were cool". Then it went in for a high-five/extended secret handshake thing. It was awkward.