I engaged TAC and we discovered that thought it was enabled, 11r wasn't functioning at this particular location. In the process of troubleshooting, the WLC rebooted itself. The crash log showed that the "cryptoPOST" , "arci-cli-helper " , "fpcli" and "nanny" modules crashed. TAC is still investigating root cause but here's the strange part: 11r is now working and the apple clients are roaming without issue.
So we inadvertantly solved one issue and discovered another. It may be due to the fact that the WLC uptime was approaching 2 years.