Elemental Invocation

Possibly a bug or intentional. With 1 Comet on my entire skill bar, it uses 20% energy to cast. With 3 on my bar, even though they aren't attached to Elemental Invocation, it requires 60% to cast it a single time. Was this intentional or a bug?

Just bumping this because this takes away from some diversity in builds. If it was intentional, I get it, but I have a feeling it wasn't.