updated 04:21 pm EDT, Wed July 2, 2014
Solves issues with video editors, multiple displays
This Monday's OS X 10.9.4 update appears to have made undocumented fixes to rendering problems with the 2013 Mac Pro, users say. Under v10.9.3, people running video editors like Adobe Premiere Pro and Blackmagic DaVinci Resolve were encountering problems such as crashes, freezes, pink and green lines in exported clips, and videos stalling during the export process. Posts on Adobe and Blackmagic's forums indicate that after updating OS X, video output is back to normal.
The v10.9.4 patch has also solves some complaints about multiple displays. Issues with USB display adapters may remain, though.
Officially the update deals with Macs failing to automatically connect to known Wi-Fi networks, as well as systems not waking from sleep reliably. It also includes Safari 7.0.5.