As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB OUT FROM DFW ALT WINDOW LOCKED OUT AT 50,000'. ALERT SOUNDED INTERMITTENTLY. ALL OTHER FUNCTIONS OF THE MCP WORKED NORMALLY. RAN QRH MODE CONTROL LOCK UP CHECKLIST. UPON RESETTING C/B'S ALL MCP FUNCTIONS RETURNED TO NORMAL OPS INCLUDING ALT ALERT WINDOW. GROUNDED - YES. FOUND MCP ALTITUDE HOLD AND ALTITUDE REF FAULTS FROM LAST FLIGHT. PERFORMED DFCS ALTITUDE ALERT TESTS REF BITE GROUP 15 PER AMM 22-11-00, ALL TESTS OPS NRML W/ NO FAULTS.