I also created a bugreport.apple.com (16269716) which was promptly marked duplicate of (16314844):
Summary:
When an HDMI device is connected to the 2011 Mac MIni (with Radeon GPU) on boot, the HT6139 update (to OS X 10.9.2 with OS X Server) will cause the computer to stop at a gray screen (no mouse visible).
Steps to Reproduce:
1. Install OS X 10.9 on a 2011 Mac Mini (with Radeon GPU)
2. Install OS X Server
3. Install XCode (not sure if necessary)
4. Install 10.9.2 update
5. Disconnect/disable HDMI display
6a. Wait for the App Store to check for updates
6b. Remote desktop in and use the App Store to check for updates
7. Reconnect/enable HDMI display
8. Install update HT6139
9. Reboot
Expected Results:
Computer boots normally to Mac OS X login screen.
Actual Results:
Computer boots (and gets eternally stuck on) a blank gray screen with no mouse pointer, computer seems fully running via remote access
Version: OS X 10.9.2 (13C64)
Server.app 3
Notes:
Discovered work-around: boot without HDMI device attached, then attach HDMI device. Not sure if related, but Screen Sharing is now not showing the correct colors after applying this update. (see attached screenshot)
Configuration:
This only occurs on a 2011 Mac Mini with Radeon graphics after HT6139 has been applied.
Attachments:
'Screen Shot 2014-03-08 at 01.58.08.jpg' was successfully uploaded.