Oh nevermind, just read back and saw that. Guess it pays off to read, doesn't it?
It looks like you know what you're doing with the commands, but before what I would always do when spoofing my MAC was separate the commands for changing the MAC and bringing the interface up again into 2 separate commands. I'd say try that to see if it works, but I doubt it will make a difference.
Not sure if it matters but what kernel are you running?