TL;DR: I’ll agree to disagree.
I assume a software killswitch works in effect the same as a hardware killswitch (with the difference that you can trust the hardware killswitch better than the software killswitch as it is a galvanic isolation). Apparently it does not, then that is a bug in Android. It probably won’t get fixed though (“working as intended” 
) , while the reported bug might get fixed.
Thanks for the report, I’ve added it in the list here in the thread: Improving the software of FP3