As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT 1906, PHL-BDL: AS FLIGHT TAXIED IN TO THE GATE, THE CREW STARTED THE APU. SMOKE BEGAN TO FILL THE CABIN AS PASSENGERS WERE LEAVING THE AIRCRAFT. UPDATED 8/3/07: PILOT REPORT INDICATES THAT WHEN CHANGING FROM GROUND POWER TO EXTERNAL POWER, POWER DROPPED OFF LINE, THEN THE CABIN FILLED WITH SMOKE. MAINTENANCE REPLACED THE EXTERNAL POWER MODULE. NO FURTHER FAULTS.