Apple has posted a GarageBand Update, 4.1.2. The update "improves overall stability and addresses issues with the automation of software instrument parameters, FireWire and USB based audio devices and Magic GarageBand," according to Apple on Monday.
The update is now appearing in Mac OS Xis System Preferences -> Software Update. It is about 19 MB.
The Apple GrarageBand 4.1.2 support page provides a direct link to download the update package.