A B757 OVERSHOT ITS ASSIGNED ALT OF FL190 BY 400 FT. ACFT HAD BEEN ON AUTOPLT AND AT A HIGH RATE OF CLB.

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CAPT WAS HAND FLYING. AFTER CONTACTING DEP WE WERE CLRED TO 10000 FT ON A N HDG. PASSING THROUGH 8300 FT MSL; ATC TOLD US TO LEVEL AT 8000 FT. CLB WAS STOPPED AND STARTING DSCNT TO 8000 FT WE WERE RECLRED TO 10000 FT WITH A 120 DEG TURN TOWARDS THE E; AWAY FROM ANOTHER ACFT AT 10000 FT. ZDC LATER CLRED US UP TO FL190. THE ALTIMETER SETTING WAS 29.52. DUE TO TFC; AUTOPLT WAS ENGAGED. THE ACFT WAS LIGHT AND 'ALT CAPTURE' OCCURRED AT 17000 FT. AT 17300 FT ALTIMETER WAS RESET TO 29.92. REACHING FL190 ACFT LEVELED OFF. HOWEVER; IT CONTINUED UP TO FL193; AT WHICH TIME THE ALT ALERT SIGNALED US THAT A DEV HAD OCCURRED. ATC ALSO QUESTIONED US BECAUSE THEY SHOWED US AT FL194. IN FACT; BY THIS TIME; WE TOUCHED FL194. ACFT WAS MANUALLY FLOWN BACK TO FL190 WHICH WAS THE ALT SET ALL ALONG IN THE MODE SELECTOR PANEL. BECAUSE THE AIRPLANE HAD BEEN ON AUTOPLT AND WE WERE LOOKING OUTSIDE FOR TFC AND THE SUN WAS RISING IN OUR EYES; I FAILED TO NOTICE THE ALTDEV. WE CALLED OUR MAINT BASE; SUSPECTING THAT THE LARGE ALTIMETER DIFFERENCE WAS TOO LARGE FOR THE AIRPLANE SYS TO ACCOMMODATE IN JUST A FEW HUNDRED FT (GOING THROUGH 17000 FT TO FL190); PARTICULARLY AFTER ENGAGING IN THE ALT CAPTURE MODE. THEY THOUGHT SO; TOO. THIS IS SOMETHING TO REALLY PAY ATTN TO WHEN TRANSITION LEVELS AND LEVELOFFS NEAR THEM INVOLVE LARGE DIFFERENCES IN ALTIMETER CHANGES; ESPECIALLY WHEN NOT HAND FLYING; BUT RELYING ON AUTOMATED SYS. I DON'T THINK THERE WAS A CONFLICT WITH ANY OTHER ACFT.