Light2D, Mask, Mix
Sometimes a light2D set to mask or mix will seem to completely ignore another light. Sprites beneath this light that's ignored will have their edges brightened but nothing else (the mask is totally dark, but similar results occur when its color is changed.) The problem appears to occur when the other light2D node is first created: sometimes it will work with the mix/mask light, and sometimes it will not. Worse, sometimes it works in the editor and not in-game, and vice versa. Post-creation, the problem is consistent; if a light2D is to be ignored by the mix/mask light, it will always be so. Removing the mix/mask light, everything returns to normal. Even duplicating a functional light can frequently spawn an ignored light. Moving the mix/mask light around in the hierarchy sometimes changes things.
So are the mix and mask modes for light2Ds broken or is there something I'm missing?