Failsafes might be the key.

I love Spektrum, but the 5 and 6 aren't surface Txs even though they can be used as one. Horizon has a lot at stake with liability and swinging props. There's tons of threads of people chewing up hands and legs, so they build safety measures into what they can. Usually nothing will work until the throttle is set all the way to zero. Maybe between the self centering stick and a failsafe, something is being triggered on shut down.

I'd look over your DX5 manual and see what it has as default. I know there are ways to program them out of failsafe.