AP 3.6.0: Crash detection triggered in flight after takeoff and disarmed flying plane

Ok, first I'll start with the good news: the resulting crashes were soft and did not cause damage (but I also didn't trust AP and used a smaller throw away plane, just to be sure :) ).

https://youtu.be/Y7B0IwQUItM shows the problem:

1. switch to auto
2. throw plane
3. auto takes over, starts the motor
4. just after that it detects a crash while the plane is in flight and disarms the motors
5. plane goes down, and thankfully lands ok

grep CRASH 23.txt
CRASH_ACC_THRESH 0.000000
CRASH_DETECT 1.000000

I did not touch the CRASH options. so those are default.
I don't see why crash detection would trigger if CRASH_ACC_THRESH is 0.
Obviously triggering in flight is bad, thankfully it happened in a way that it was not a big deal in my case.
23_auto_crash_disarm.txt

Full log (auto is at the end of flight): http://marc.merlins.org/tmp/23_auto_crash_disarm.bin