OVERSHOT ALT XING RESTRICTION AT BVL OF 29000 FT FOLLOWED BY AN UNRELATED TCASII AT 21000 FT.

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WE WERE GIVEN CLRNC TO CROSS BVL AT OR ABOVE FL290 THEN DSND TO FL210. I MADE A MENTAL CALCULATION THAT WE SHOULD START DOWN AND DID SO. THERE WAS A CHK PLT GIVING ME A LINE CHK AND WE WERE DISCUSSING SOMETHING OR OTHER AND I NOTICED WE WERE AT FL250 AND HAD NOT PASSED BVL. BUSTED CLRNC BIG TIME! I DISCONNECTED AUTOPLT AND STARTED CLB AND TOLD COPLT TO CALL ATC AND TELL THEM. THEY REPLIED NO PROB; JUST CONTINUE DSCNT TO FL210. WE DID SO AND JUST AT LEVEL OFF GOT AN RA; 'DSND; DSND.' I IMMEDIATELY COMPLIED. AFTER DSNDING 300-400 FT THE RA CHANGED TO 'CLB; CLB.' THE CHK PLT SAW THE COMMUTER PLANE WHO WAS NO FACTOR. THE CTLR SAW US DSND AND WE TOLD HIM WE HAD AN RA. WHEN WE GOT TO FL210 AGAIN THE RA CHANGED TO 'MONITOR VERT SPD.' I DID EXACTLY WHAT THE TCASII SAID TO DO AND IT GAVE CONFLICTING INSTRUCTIONS. I NO LONGER TRUST IT. WE NEED TCASIII NOW. THE TCASII INCIDENT SEEMED INDEPENDENT OF THE ALT BUST BUT MAY HAVE BEEN CONTRIBUTED TO BY IT. I DO NOT THINK THERE WAS ANY LOSS OF LEGAL SEPARATION.