When the head is loosened, main power is disconnected. However, small amount of power through the switch can power up the light. In this state, the light is in reset mode. If you keep pressing the switch while the main power is disconnected, it will begin reset procedure after blinking for about 3 seconds.
If you loosen the head of TS10, your light will not turn on (and drain the battery). But it can reset the light if pressed more than 3 seconds.
I have seen this behavior in KR4 and TS10, but NOT in FW3A. My FW3A switch is completely disabled when I loosen the head.