CE650 FLT CREW LEARNS THE IDIOSYNCRASIES OF THE CE650 FMC DURING THE JAWBN 1 ARRIVAL TO BFI AFTER CHANGING THE LANDING RWY. JAWBN CROSSING RESTRICTION IS NOT MET.

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WHILE DSNDING INTO BFI ON THE JAWBN1 ARR; WE DSNDED BELOW ONE OF THE PUBLISHED ALTS. IT WAS A MANDATORY ALT PUBLISHED ON THE CHART; AND WE WERE TOLD TO DSND VIA THE ARR. THE ALT WAS SUPPOSED TO BE JAWBN AT 16000 FT; BUT WE MANAGED TO CROSS IT AT 14000 FT. ATC CTLR TOLD US NOT TO WORRY ABOUT IT AND JUST LEVEL OFF AT 14000 FT. HOW DID IT HAPPEN? THE JAWBN FIX HAS 2 DIFFERENT ALTS PUBLISHED -- 1 FOR LNDG N (16000 FT); AND 1 FOR LNDG S (11000 FT). WHILE ENRTE TO BFI; WE LOOKED AT THE WX; AND THE WINDS WERE FAVORING LNDG S. WE SET THE FMS UP TO LAND S; AND THE 11000 FT ALT WAS AUTOMATICALLY PUT IN THE FMS. WE DILIGENTLY VERIFIED THE XING ALTS IN THE FMS FOR ACCURACY. SHORTLY AFTERWARDS; WE RECEIVED THE ATIS; AND IT SAID THEY WERE LNDG N. WE CHANGED THE FMS FOR A N LNDG; BUT WE NEGLECTED TO VERIFY THE ALT AT JAWBN CHANGED FROM 11000 FT TO 16000 FT. WE MUST HAVE GOT BUSY; AND I SAW THE HDG TO DEPART THE LAST FIX ON THE ARR 'DID' CHANGE WHEN WE SWITCHED THE RWY. BECAUSE OF THIS; I ASSUMED THE XING ALT ALSO CHANGED; BUT IT DIDN'T. I NOTICED THE ERROR AS WE DSNDED THROUGH ABOUT 14500 FT. I FESSED UP TO THE CTLR; WHO SAID TO LEVEL OFF AT PRESENT ALT (14000 FT); AND THAT IT WAS NOT A BIG DEAL THIS TIME. SHE ALSO SAID TO BE CAREFUL IN THE FUTURE. I'M RPTING THIS FOR SEVERAL REASONS; BUT ONE IS BECAUSE OF AN FMS FLAW THAT WAS A CONTRIBUTING FACTOR. I DUPLICATED THIS ON THE GND; SO I'M POSITIVE THE FMS WILL NOT CHANGE PUBLISHED ALTS WHEN YOU SWITCH RWYS (AT LEAST NOT FOR THE JAWBN1 ARR INTO BFI). ALSO; I FIND IT ODD THAT THE OUTBOUND HDG 'DOES' CHANGE WHEN YOU SWITCH RWYS. SO; IT CHANGES HALF OF WHAT NEEDS TO CHANGE. WE SAW THE HALF THAT DID CHANGE; AND INCORRECTLY ASSUMED IT ALL CHANGED.