Ground crew reported witnessing the aircraft roll forward after the tow bar was disconnected.

Narrative

We pushed off a widebody aircraft. I was the wing walker on the left side of the plane. Everything went smoothly with the pushback until the pushback driver stopped the plane and signaled that the brakes were set and ready to disconnect. I disconnected the tow bar but the towbar was jammed and did not release from the plane. The pushback driver gave me a signal to step back. He put the plane in gear and the towbar released down from the plane. The plane then rolled forward and over the towbar.I witnessed the aircraft roll forward and saw the towbar under the nose gear. It seemed to be a miscommunication between the pushback driver and the pilot. As a wingwalker; I have no communication with the pilot and only hand signals with the pushback driver. So I do not know what decisions led to the event. The Crew Chief was notified by me and crew chief notified the manager. Maintenance arrived shortly after. Event could have been avoided if I had a cordless headset. I could have communicated to both the pilot and pushback driver not to release the brake.