Spellthief's Edge bug

I was playing Karma and realized, that if you use your Q on 2 enemy champions at the same time with a Spellthief's Edge, you only get the Spellthief's Edge proc on one target. I tested it out on dummies in training mode, and the same thing happened. Don't know if it's supposed to work like that, but it feels weird that you don't get the proc for hitting both.