Incinerate gaining stages at half-rate

Hello,

From current research I find there's been an ongoing bug (if you can call it that) with the way incinerate gains stages. It's been apparently ongoing for a few years.
The skill basically gains stages at half the rate at which flameblast, a skill with the same cast speed and similar description, does.
With the introduction of the new transfigured versions of incinerate which emphasize gaining stages quickly could there be clarification on this being an intended behaviour of the skill or an actual bug? and if the latter, can we expect a fix for this?

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