Heft (Support Skill Gem) is being applied twice

I have seen several threads talking about Heft, but I haven't seen any mentions to the fact that Heft is being applied twice.

The gem reads:

"Supported Skills have 30% more Maximum Physical Damage"

The expected outcome, based on the wording ("more") is that it would be applied multiplicatively with the rest of multiplicative damage bonuses. However, it's also increasing the base max damage. It's doing both things.

Example:

* Weapon has base damage of 30-100. Heft takes this to 30-130 (30% increase of max damage).

* Increases to weapon damage are applied (passives, etc.)

* Multiplicative damage increases are applied here and Heft is applying again. So if in example we're now dealing 600 - 2600 damage, Heft will be applied to the max damage, resulting in 600 - 3380 damage.

This is leading to a much higher scaling than intended, which is why some skills are dealing so much damage when using this gem.

---

I discovered this while researching minion scaling. I can provide some exact numbers:

* Skeletal Sniper level 33.
* Increased minion damage is 391%, plus 40% from weapon.
* Total crit chance is 12.50%.
* Crit bonus is total of 327%.
* Increased attack speed is 33%.
* Using Martial Tempo, Feeding Frenzy, Brutality, Heft and one extra that does not affect calculations here.

Expected damage would be:

Increased applied: 7316 - 13211
After gems: 12525 - 30140 (Heft is applied here based on the 'more' wording)
With crit, attack speed and martial tempo: 33475 DPS.

However, because Heft is applying twice, what happens is that the base damage is changing. The base damage at level 33 skill gem (level 66 skeletal sniper) is 1341-2480. However, the 2840 is becoming 3224, so the damage range is 1341 - 3224.

Tooltip values then are:

Increased applied: 7316 - 17156
After gems: 12525 - 39142 (Heft is applied again here!)
With crit, attack speed and martial tempo: 40k DPS, which matches in-game values.

The only way to match my values and tooltip values is by applying Heft to the base damage and then as a multiplier to max damage.

I also tested with POB and POB is also calculating it as I was, not taking into account this bug.