I have noticed since the release of Heart of Fire that when using the Celestial Stag mount power, I do not see any effects though the timer counts down from 60 seconds. For instance, I can use the power ten times and maybe get the visual effects and the damage to show up three, four times. When I mention to my friends if they can see the effects/damage on their screens, they cannot. The location where I use the mount power makes no difference, whether in a dungeon or running dailies. Sometimes it works; most of the time it doesn't.