Viscous Puddle Punch & Melee Charge Interaction

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Not sure if this is expected behaviour or not, but:
The "Melee Charge" item is buffing Viscous's Puddle Punch ability.
Puddle Punch does NOT put Melee Charge on cooldown.

If I manually heavy melee, Puddle Punch does NOT get the benefit whilst it's on cooldown.

I'd expect behaviour to be either:

Puddle Punch puts Melee Charge on cooldown
OR
Melee Charge does NOT benefit Puddle Punch