The issue was spotted shortly after 1.0.4 went live but Blizzard didn't want to hotfix but instead await a full patch release to give players "proper notice" as it will render some builds weak.
Obviously the appeal of a rune delivering 1500% weapon damage over 3 seconds couldn't be ignored by many, but it was never meant to be that powerful.
Blizzard community manager 'Lylirra' posted on "...we will be fixing a bug with Trail of Cinders that is causing the rune to deal five times more damage than intended. As a result of this fix, the amount of damage done by Trail of Cinders will be reduced from its current value (1500% weapon damage over 3 seconds) to the value we originally designed for 1.0.4, which is 300% weapon damage over 3 seconds.":
"While this bug was discovered very quickly after 1.0.4 released and is capable of being hotfixed, we didn't want to move forward with the fix without giving players proper notice. We also know that players are having fun using Trail of Cinders in their builds, so -- although this is an important issue we want to address -- we're opting to wait for the next client patch to make any adjustments."
The team are well aware that some builds out now will get destroyed. "Ultimately, we want to continue to provide players with more build options and ways to feel creative with their skill/gear selections, but not at the expense of going against our design goals or creating situations which can encourage players to limit themselves defensively."
The current level of power Trail of Cinders enjoys violates their design philosophy for Discipline, they continued.
"Discipline-based skills were never intended to trump Hatred-based skills when it comes to dealing damage. Instead, Discipline should be something you build up and save to use defensively, or to provide utility in addition to dealing damage. Allowing Trail of Cinders to remain in its current form goes against this philosophy, and in addition creates risky scenarios for players (after all, if you’re incentivized to spend all your Discipline doing damage, it won’t be available when you need it to keep yourself alive with skills like Smoke Screen or Shadow Power)."
At present those who are a-okay with the white knuckle ride of burning up all their Discipline with Trail of Cinders needn't worry just yet of having their toy taken away. Blizzard are yet to stamp the 1.0.5 patch with a date for release so get all the loot runs in that you can people!