It's called a "powerback," as opposed to a "pushback."

The pilot will tell us FAs that this is going to happen. Usually we wait with the safety announcements until this is over. We might fall over in the cabin!

It's very common, but seems to be even more common at the new terminal.

Less ground people working = less tugs in use, and less groundpeople to signal the plane into "brakes up" at the gate.