AUTOPLT FLARES BUT FLOATS AND BALLOONS RATHER THAN AUTO- LNDG AS EXPECTED REQUIRING THE CAPT TO GAR.

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WE WERE ON PAX FLT FROM TPE TO NRT. FO FLYING. FO ELECTED TO DO AN AUTO-LAND AND I HAD NO OBJECTION. WX WAS CAVU AND LIGHT WINDS. EVERYTHING WAS NORMAL UNTIL ABOUT 8 FT. I WAS SO COMPLACENT I WAS WAITING FOR THE WHEELS TO KISS ON. THE ACFT FLARED; THEN A SMOOTH; VERY SLOW CONTINUOUS PITCH UP OCCURRED. THE FO WAS TRYING TO OVERRIDE THE AUTOPLT RATHER THAN DISCONNECT IT. AT THIS TIME I WASN'T SURE WHAT WAS HAPPENING AS I SAW THE FO HAVING AN AMAZED LOOK ON HIS FACE; THINKING I WAS DOING SOMETHING. AT ANY RATE WE WERE NOW ABOUT 20 FT UP; NOSE HIGH AND DECREASING AIRSPD. I LITERALLY SLAMMED THE THROTTLE LEVER FORWARD; INITIATING A GAR. AS I FELT NOT ENOUGH CEMENT WAS LEFT TO RECOVER FROM THE POS I WAS IN. NRT TWR QUERIED THE REASON FOR THE GAR AND MY RESPONSE WAS 'WE FLARED HIGH AND I FELT I HAD TO.' NO OTHER QUESTIONS OR COMMENTS WERE MADE TO ATC ABOUT THE REASON FOR THE GAR. RWY 34 IN NRT IS NOT A CAT II OR CAT III AND I NEGLECTED TO NOTIFY THE TWR OF OUR AUTO-LAND ONLY BECAUSE THE WX WAS NO FACTOR AND THE OP WAS SO ROUTINE. IN RETROSPECT; IT APPEARS THAT THE ACFT WAITING TO LINE UP DID IN FACT INTERFERE WITH THE GLIDE PATH XMITTER AND OUR RECEIVER. A LOG BOOK ENTRY WAS MADE AND THE 747-400 CHIEF PLT IS CHKING THE HISTORY OF THE ACFT. IT REALLY WASN'T A PROB BUT I WAS SO 'LAID BACK' AND EXPECTING ENTIRELY DIFFERENT RESULTS. IT COULD HAVE BEEN.