Well, I’m not much help here. The only other things I could suggest are try the Wavelab 8 or Wavelab 8 Elements demo. See if it happens there.
Not responding to the “scroll during playback” setting is wrong. See if that happens in Wavelab 8. Also, the erratic backward movement is what would happen if you had stuck left-arrow keys, the ones in the number pad (depending on the status of the num-lock key - try toggling that) and the left-arrow key in the standard keyboard. If you hold down the left arrow key(s) you get the cursor movement you’re talking about.
Are you and your co-worker both using keyboard-mouse extenders, usb or ethernet? Any other hardware or software in common?
Maybe PG would have a fix or other troubleshooting. Or you could file a Steinberg support case if you haven’t already.