Kennen's Lightning Form does not give as much movespeed as intended

I am not sure if this is just a typo on the tooltip or what-not but I find it very aggravating when i go into Lightning form and everytime i feel played for a fool when i get half of the speed boost that the tooltip says. The tooltip says that while Kennen is in Lightning Form, he gains 335 movespeed. His base move speed is 335 as well so his effective movespeed should be DOUBLED. I have found time and again that this is not true. I press E and my peak speed without enhancement or slow comes to around 565. This is a far cry from the 670 i should be getting.

I would like to hear back from you guys whether or not this is one of those numerous tooltip bugs or if it really is supposed to double your movespeed. I really like Kennen and I want him to work like intended.