Users of a Thunderbolt equipped Mac will want to head on over to the Apple Support pages and grab the latest firmware update. It's not a huge update, in fact the download is just 1.22MB in size, but does promise stability fixes for Thunderbolt and for Target Disk Mode. And we'll always welcome stability fixes.
A restart of your Mac will be required following install, and to grab the new firmware hit the source link below.
Source: Apple Support