Ok, I've done some more work but I'm still having this issue. I think the motor may have a problem.
I tried a Phoenix Icelite 75 ESC, set it up, was able to set different brake settings, works but still not braking.
Took the plane back home, started to test, motor jerked back and forth convulsively and smoke rose from the Phoenix! Burned out, no longer works. Plugged the Hyperion ESC back in, works as before, no brake, continues to run after throttle down. Tried a different radio, tried a simple AERO program, tried programming "Throttle Cut" switch which does exactly that, zeros the throttle. All with the same old results, no brake.
So can the motor continue to draw power even when the radio and ESC are sending 0 throttle to it? I've switched out everything but the motor at this point, but this puzzles me, I wouldn't think the motor would be able to do that.
Searching in RCGroups I see that some others have had similar issues and a possible explanation is that a short in the motor can burn out the ESC FET and it can no longer regulate the power. I can't think of anything else to do at this point but buy a whole new motor and ESC.