Along with its new lineup of cheaper, truncated Thunderbolt cables, Apple has issued a small firmware update for its mid-2012 MacBook Air notebooks. The update primarily addresses two problems, the first of which is a freeze that can happen when unplugging Thunderbolt devices on standby, while the second is an improper boot in Windows.
The update is a small 4.67MB download that should be available if you choose Software Update from the Apple menu, but can also be downloaded separately from the Apple support Web page.
When installed, the EFI ROM on the system will have the version string of MBA51.00EF.B02, which can be checked in the System Information utility in the Hardware section next to "Boot ROM Version."
As with any firmware update, it is important to follow the onscreen instructions for updating the system, and be sure your system is plugged into a reliable power outlet. And as always, be sure to first back up your system before applying this or any other update.