Kennen E inconsistent with Celerity Rune

Kennen's E says it doubles his base MS, which means %speed bonuses which scale off base MS will also double.

The Celerity rune says it gives bonus AP/AD based off of Bonus Movespeed, so Kennen's E should approximately double the bonus from Celerity assuming he has no flat MS bonuses like from boots. However it game it gives a much larger bonus, (going from say 6 AP to 28 AP when activating E) indicating that Celerity is treating the doubled "base MS" as bonus MS instead.

This seems like it might be an intentional interaction and the tooltip of Kennen's E might just be worded improperly.