While playing on a lightsout server with a friend fullmoon event did some weird things. First off, once it became fullmoon, those that were above ground will not be able to see anything outside of the light (like a normal night, just with full moon colourcubes applied). When disconnecting/rejoining during the full moon the world will light up as normal, however grue will still attack you outside of a light source.
After the fullmoon passed, darkness became bugged. Grue doesn't attack you, the world remains visible as if its day (which goes back to normal on disconnect/reconnect but still grue does not attack you).
The server did have caves enabled.
Make a lights out world, wait till fullmoon appears at day 12.