If there is a Theta Vent or an Eject Warp Plasma effect in the area it will hide other Plasma based effects (Plasma Torpedoes, other eject warp Plasma, other Theta Vents) You will see people using those powers but you will not be able to see those effects.
Steps to Reproduce:
1: Have Eject Warp Plasma or Vent Theta Radiation Console on your ship, or on another players' ship.
2: Activate either Eject Warp Plasma or Vent Theta Radiation
3: Fire either Plasma Torpedos, other have some one else activate an Eject Warp Plasma or Vent theta Radiation.
This is noticable the more effects are on screen (Pets, Mines, etc..) and effects both PVP and PVE.