It cannot therefore be a safety thermal cutout.It is either some kind of voltage or bec cutout so I'll leave it up to those who actually use these escs and know the other quirks.

It may help them if:
[ul][*] you say what you mean by turning off the circuit.[*] say at what position the esc switches.[*] confirm the receiver pack is fully charged[*] observe what happens with bec power from an esc.[*] observe what happens with the working esc disconnected[/ul]

best of luck!