As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) CLIMBING IN SPEED MODE WITH THE SPEED BUG SET AT 250 KNOTS THE SPEED BUG MADE AN UNCOMMANDED CHANGE TO 79 KNOTS. NO VERTICAL SPEED CHANGES HAD BEEN MADE RECENTLY ALTHOUGH WE WERE MAKING LATERAL CHANGES OF HEADING AND ALSO INTERCEPTING AN FMS COURSE AROUND THE TIME IT HAPPENED.