Maelstrom: Gathering storm not working as expected

Killing an enemy has a chance to create a stack of Maelstrom. This effect has a 2 second cooldown. Chance On Kill to Cast Maelstrom: 5% per point.

The expected behavior is that the 2 second cooldown is incurred after maelstrom activates once.

However this mechanism seems to incur the 2 second cooldown even on a failed roll where the ability does not activate, meaning this is a 5 point investment that cannot even keep a single stack of maelstrom active on the player.