Apple released Thunderbolt Firmware Update v1.1 for the mid 2012 MacBook Pro on Tuesday. The update improved compatibility with some Thunderbolt cables that were preventing peripherals from working properly.
MacBook Pro gets a Thunderbolt Update
According to Apple's terse release notes, "This update addresses an issue with MacBook Pro (mid 2012) and some Thunderbolt cables that may prevent bus-powered Thunderbolt devices from functioning properly."
The update requires OS X 10.7.4 or higher and is available through the Software Update app, or as a downloadable installer via the Apple Support website.