Flare Bug
From WikiRaider
The Flare Bug is one of the annoying bugs. It appears only in the Custom Levels (and maybe in The Last Revelation).
If you get this bug, flares might not work, as long as Lara is holding them. They will only light up the room, if you throw them on the ground.
This bug appears, if a Level Builder hat too many active Fire Emitters in his level. (The magical number seems to be 32.) You can avoid the flare bug by turning off flame emitters, when leaving a room. (Anti Trigger)