Glad the OP didn't get hurt
for all the rest of us - gear WILL malfunction - especially when we start modifying it to use for unintended purposes. Doesn't mean we shouldnt use it it means to take precautions and know the risk.
ALWAYS, I repeat ALWAYS, secure your tether and lineman's before stepping onto any platform (spikes, ameristeps or cast platform) the #1 cause of tree stand falls is transitioning to and from platform to climbing method. And if you are not using a lineman's to climb, then consider this a friendly cyber smack to the back of your head "what the hell are you thinking" post.