Tyreal's Swift Retribution Talent Doesn't Always Work

Tyreal’s level 7 talent, Swift Retribtion, is supposed to give +20% movement and +25% attack speed, but I noticed that it doesn’t always work. I’d say about 50% of the time, I don’t see the attack speed buff. I’ve tested it in the test realm and it doesn’t always proc. What gives?

You have to walk through the wake that Smite leaves behind to trigger the buff. The description is worded poorly.