Bladefall of Trathus with Whispers of Infinity ES Cost

Whispers of Trathus costs 5% of max mana per second. For a build with about 1000 mana that's 50 mana per second. Last league when using Whispers of Infinity, you convert the cost to 50 ES per second.

But this league, the skill costs 5% of ES per second instead, i.e. for a build with 10000 ES and 1000 mana it costs 500 ES per second instead of 50 as it would last league.

This is not mentioned in the patch notes and so it must be a bug.