Currently the tooltip or skill application itself for inner flame is currently bugged or broken.
The skill tooltip is supposed to apply 10% fire and lightning damage per second inducted for a total of 30%... but... when used, it will apply a maximum value of 18% with it fully traited, 16% with 2 points and 14% with only 1 point traited into it.
Just figured I'd pop this up there to see if its something that could be fixed in a reasonable timeline either by adjusting the tooltip or making sure it properly applies the 30%.
As a note, this problem only came up with the release of Before the Shadow, so its not an old bug or problem, but a very recent one.