Frost wall and spark

I was fighting a spark witch earlier today and I tried using frost wall to stop the sparks from hitting me. The witch I was fighting had spark supported with fork, and when the sparks hit the frost wall instead of disappearing they forked. The forked projectiles were invisible. When spark hits a frost wall when it isn't supported with fork it just disappears.

I was wondering if it's intended that spark supported with fork forks when it hits a frost wall, since it doesn't fork when it hits other objects that aren't enemies. At the very least the ability is bugged, since the forked projectiles are invisible.