Upgraded from a fc17 x86_64 install with 304.51 to a clean install of fc20 w/ 304.116 (same symptom with RPMFusion 304.108).
Now I only have three displays functional. I’ve had this card for several years and it has always worked smoothly, but with this upgrade, it no longer functions as a quad-head card.
The Xorg.0.log output clearly shows it seeing all four monitors, it just looks like it never tries to activate the second monitor on GPU-1.
Bug report file linked below.