Add Movement Input sideways causes jitter

Hi

If I try to add some movement input for the sideway axis of my character he starts to jump while moving… Just like on the video:
https://drive.google.com/file/d/0B65...ew?usp=sharing

Going forward and back works just fine, going sidewys = jumping.

Orient rotation to movement is off. Movement mode is Walking. Reducing the bounciness and/or friction doesn’t make a difference. Changing the mode to Flying kind of solves the problem, but as I would use the Flying mode later on I would rather not go with using flying mode for ground level movement.

So what can I do to move my character, on the ground, sideways with no jitter like on the video?