The camera operates seperate from the PIR. It should function in all modes - flash, no flash, auto, etc. Hope this helps. Most people will use the forced setting. I personally use the forced for all pics, especially when facing the rising or setting sun. The flash will fill in the shadows better making a avg. pic outstanding.
I thought i read somewhere that it needs to be set to forced flash so the PIR sensor will reset before the camera does for some reason. I know i run forced flash on my round on/off switch model and it works great. Just not sure about the BF model??