If you take Swashbuckle (pangolier) and Infernal Blade (Doom), you might expect that this combination would apply Infernal Blade's proc to the first target hit by Swashbuckle. You'd be wrong.

Instead, Swashbuckle will not apply Infernal Blade's effect, but will (a little more than half of the time? It didn't appear to be related to whether Infernal Blade was on cooldown or toggled) consume Infernal Blade's 40 mana, per unit, per time Swashbuckle hits that unit.

Since Swashbuckle is a large AoE that attacks 4 times, this can easily consume upwards of 1200 mana, for no benefit.

I'd imagine that this underlying issue may also exist with orbs such as Frost Arrows and Poison Attack, but that they would also at least apply their effects.