When you change forms (example switching into dracthyr dragon/human or using a race changing toy) the Shadow Flame weapon illusion loses glow effects clearly shown in this example I made here.
First picture is before and second picture is after I changed to a dragon and back to human.
The first picture is clearly very bright and glowy while the second picture is dim and lost particle effects.
The only way to fix it is to log out and back in again and as soon as you change forms again it loses its glow again.
Also the same bug happens when you first apply the illusion to a weapon, it stays dim until you relog.
EDIT: seems to be happening to pretty much every single weapon illusion you apply even older ones from past expansions.
