Vayne's tumble double-stacking silver bolts

Is tumble intended to apply 2 stacks of silver bolts? With her Q no longer benefiting from critical effects, this would be a good alternative to keep her DPS roughly in line while reducing her burst potential which I assume was the point of the change. But if this is a bug, her laning and team-fight is actually worse. I haven't seen any official mention about it yet, so I figured I'd post here.
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