Sorry about the major post as well... but after thinking, yeah it's a critical not a major. I'll repost the same thing as other thread.
I was at 386 movement speed.... then went down to 376 movement speed when I used my Q on an enemy champion... it also happened on minions.
When I just cast Q regularly, it doesn't hinder her movement speed at all... only when you hit something. It doesn't show this in her tool-tip... so this has to be a bug.