This can’t possibly NOT be a typo in the code. I’ve tested this with the MkVII and MkVI Heavy Swords.
To be clear, we’re talking about the Light attack that immediately follows the Special attack. That Light is different from all others in term of the usual Light combo.
For example, with a MkVII Heavy Sword (360 stat) a normal Light does 42 or 48 on Flak. The Light that follows up a Special attack does half that : 20 damage.
Similar thing with unarmoured and infested damage, it’s cut by about half the usual. But, doing a Heavy after a special attack deals the usual amount of damage.