A320 CREW REPORTS PROBLEMS WITH ILS 33 AT BWI. ACFT ON AUTOPILOT CAPTURED FALSE GLIDE SLOPE AND STARTED DESCENT.

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IN-RANGE BWI ATIS STATED ILS 10 APCH IN USE. REVIEWED AND BRIEFED ILS 10 ON DSCNT. AT APPROX 10000 FT; BWI APCH ADVISES US TO PLAN ILS RWY 33L. MCDU WAS SET FOR ILS RWY 33L WITH APPROPRIATE MINIMUMS. WE ARE VECTORED ONTO FINAL OUTSIDE OF SPLAT LEVEL AT 2000 FT. FLAPS ARE AT 2 DEGS AND LNDG GEAR IS UP; AIRSPD 170 KTS. AFTER LOC INTERCEPT; CAPT STATES THAT HE IS NOT GETTING AN IDENT FOR THE ILS OR GS INDICATION. FO STATED THAT HIS SIDE IS SHOWING IFND (IDENT FOR RWY 15R) AND FREQ 111.7. WE ARE EXPECTING TO SEE IRUX (IDENT FOR RWY 33L) AND FREQ 111.7. DURING BRIEF DISCUSSION AND CHK OF RAD NAV PAGE; THE ACFT BEGAN A DSCNT JUST INSIDE OF SPLAT; AND PRIOR TO RUETT. GPWS ANNOUNCED 'DON'T SINK;' FOLLOWED IMMEDIATELY BY 'TERRAIN; PULL UP.' CAPT IMMEDIATELY RESPONDED TO GPWS WITH TOGA AND PITCH UP. AS CLB COMMENCED; THE AIRSPD WENT BRIEFLY INTO OVERSPD. WE HAD NO GS INDICATION ON PFD AT THIS TIME. WHILE WORKING THROUGH THE GAR PROC THE FO INFORMED TWR THAT WE WERE GOING AROUND. WE WERE INSTRUCTED TO MAINTAIN 2000 FT. AT THAT MOMENT WE WERE CLBING THROUGH 2000 FT. CAPT IMMEDIATELY MOVED THRUST LEVERS TO IDLE AND MADE A GENTLE LEVELOFF AT 2000 FT. AFTER LNDG WE DEBRIEFED THE APCH AND GAR. ONLY THEN DID WE REALIZE THAT THE INCORRECT APCH IDENT WE WERE GETTING WAS FOR THE RECIPROCAL APCH TO RWY 15R. WE SUSPECT THAT THE APCH FOR RWY 33L WASN'T ACTUALLY SWITCHED ON THE GND UNTIL AFTER WE HAD ARMED APCH. DO NOT KNOW WHY ACFT BEGAN DSCNT FROM 2000 FT. AT SPLAT THE ALT WAS CAPTURED AT 2000 FT AND APCH WAS ARMED. WE SUSPECTED THAT PERHAPS IF THE GND SELECTION WAS MADE FROM RWY 15R TO RWY 33L THERE WAS A BRIEF CAPTURE OF A GS SIGNAL AND WHEN THE SIGNAL WAS GONE THE ACFT REVERTED TO VERT SPD MODE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: BOTH CREW MEMBERS HAD COMMUTED TO WORK AND THEN FLEW TWO LEGS PRIOR TO THE CROSS COUNTRY FLIGHT TO BWI ARRIVING AT DAWN. EACH CREW MEMBER HAD OVER 7 YEARS A320 EXPERIENCE AND NEITHER COULD UNDERSTAND WHAT CAUSED THE ANOMALY THEY EXPERIENCED. THE WEATHER WAS 700 OVERCAST WITH HEAVY RAIN DURING THE APPROACH. THE AIRCRAFT LANDING BEHIND THE A320 LANDED NORMALLY AND THE A320 CREW LANDED NORMALLY ON THE SECOND ATTEMPT. THE GO-AROUND WAS INITIATED AT 1500 FEET AND A FLAP OVERSPEED OCCURRED DURING THIS MANEUVER.