I just went through the Savathun strike, killed two orange bar acolytes with the Recluse and they dropped 11 orbs of light on the ground. I'm pretty sure that masterwork weapons can only generate one orb per multi-kill.
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This happens sometimes when you go from one zone to another and make a kill quickly after. I think it happens when you do that and are still in the multikill window that would generate an orb. You can also trigger a void dragonfly effect the same way, on any weapon. It's not really exploitable because it's such an edge case, but it's always fun when it happens.