With the release of OS X 10.9.2, customers began to complain about pink horizontal lines appearing in exports. In OS X 10.9.3, the problem got worse. Now that OS X 10.9.4 has been released, these problems have largely gone away. If you are seeing artifacts in your exports and are still running OS X 10.9.3, update to OS X 10.9.4.
A user has reported that they are seeing artifacts even after updating to OS X 10.9.4, but found that they had faulty GPUs. You may want to have Apple techs troubleshoot your computer if updating the OS did not help.
More details here.