When progressing from bm_c4a1a (lab airlock on Xen) to bm_c4a1b with the flashlight on, it fails after the load and can not be turned on again, although it still plays the ‘click’ sound.
Edit: Just went back to verify. It seems the flashlight simply does not work on this map. Has no effect if on or off on the previous map. This is the map you enter from the lab airlock to the underground tunnels.
Edit2: Proceeding past the first light post causes something to trigger, which causes the flashlight to begin working again. Reloaded several times to verify. The flashlight does not activate while in the lab airlock, but proceeding down the tunnel past the first light causes it to activate every time.