Ashe and Hurricane almost certainly unintentional interaction.

Played around with Ashe in a custom today, bought a hurricane on her. When Ranger's Focus is active, Hurricane's secondary bolts are based on the damage of one of the mini arrows she fires, greatly reducing the damage of the bolts (roughly one 4th their usual damage). This is easily testable in a custom game.

EDIT: I should add that I suspect the problem is that Hurricane only fires a single bolt on attack during Ranger's Focus, rather than the 5 shots, so the single bolt is very weak.