Try this, disconnect the number 8 wire from the controller. Do they still both come on? If not there's a problem with the controller.
I'm assuming they will both still come on. You have two wires touching somewheres. Sometimes the casing comes off the wire and they'll touch. Many times it's at the valves but could be anywhere along the line. Usually above ground. Look around.
If you can't figure it, do you have a spare wire you can use for number 8 and just abandon the one you're using now.