That's very odd...I've set altitude at 100' one time right after the firmware update and it is still in place since September 1...haven't had to reset it at all as I've flown numerous times since and it is holding firm. There must be something that didn't go quite right with your update. Maybe try downloading and updating once more? If not that, I'd call Yuneec CS.
Yes, switch it off after every session. As I said, I've flown numerous flights since the update across 3 or 4 sessions. As for steps, all I've done is just set the slider to the altitude I want for RTH.
GMC, mea culpa...After thinking about this further I went and checked my ST16 again. What I had mistakenly recalled was that I had set the height my last flight at the base level of 65 feet, which is normally fine where I fly. However, I previously had set it at 100 feet but didn't check to see if it had changed because the last few flights previous, I hit RTH but was flying at 100' so the bird naturally returned at that level. So, long story short:
You are correct: Turning off the ST16 does reset the RTH altitude to 65'...but, even worse: You don't even have to turn the ST16 off to lose your altitude setting for RTH. Even simply exiting telemetry to access Pad and then returning to Home Screen, the altitude setting reverts back to the base 65 feet! UNACCEPTABLE!
Unless someone else can confirm otherwise, this is definitely a bug in the update and needs to be fixed immediately. For those of us (like here in Tennessee) who have to fly regularly around 60-70 foot trees, this is an extremely dangerous bug. So for now, this is another item I'll have to add to my preflight checklist before liftoff as well as every time I exit telemetry, much less switch off the ST16.. Thanks for bringing this to my attention, GMC!
YUNEEC, I hope you are listening!