Immediately after separation, the upper stage of Falcon 9 seems to head 30 or so degrees sideways. What causes that? Is it a problem or a feature?

Separation occurs at 4:40 in this video of the Falcon 9 SES-10 launch March 30, 2017. The image below is a frame of it, taken from the first stage about five seconds after separation, showing the upper stage wobbling.