As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS NOT GROUNDED: WHILE DESCENDING IN VNAV FROM FL280 TO FL 220 THE AIRCRAFT DID AN UNCOMMANDED LEVEL OFF AT FL 240 (THERE WERE NO RESTRICTIONS TO MAKE THE PLANE LEVEL OFF). LATER IN THE FLIGHT WHEN AT FL220 TRYING TO DESCEND TO 11000FT, PASSING THROUGH FL210, WHILE IN VNAV THE AIRCRAFT STARTED TO CLIMB BACK TOWARDS FL220 ON ITS OWN.