B-737 FLC HAS ALTDEV ON STAR DSCNT.

Narrative

I HAVE JUST BEEN CHKED OUT ON THE B737-300-500 SERIES ACFT AND HAVE JUST OVER 130 HRS IN TYPE. DURING MY FLT FROM DFW-IAH; I WAS GIVEN A COAST 2 STAR. SINCE IT WAS MY LEG; I PROGRAMMED THE FMC WITH MY FO RECHKING EVERYTHING SINCE HE HAS OVER 7 YRS EXPERIENCE IN THIS ACFT. WE BOTH AGREED THE FMC WAS PROGRAMMED PROPERLY. THE ACFT STARTED ITS DSCNT FOR THE STAR AND WAS WITHIN PARAMETERS FOR XING HOAGI INTXN AT 10000 FT AT 250 KTS. THEN AT 1000 FT ABOVE ITS XING ALT; I NOTICED THE ACFT WENT FROM A 2800 FPM TO A 4500 FPM DSCNT. I THEN JUDGED THAT THE ACFT WAS GOING TO BUST ITS ASSIGNED ALT OF 10000 FT AND WE WERE STILL 10 MI FROM HOAGI INTXN. I TRIED AT THIS POINT TO ACTIVATE THE MCP; BUT BOTH THE FO'S AND MY MCP WENT TO MASTER ARM MODE WHEN ONLY MINE SHOULD HAVE. BECAUSE OF THIS SIT THE AUTOPLT WOULD NOT RESPOND PROPERLY. I THEN DISCONNECTED THE AUTOPLT AND HAND FLEW THE ACFT. IN THIS SHORT PERIOD OF TIME WE HAD BUSTED OUR ALT BY 1500 FT. I IMMEDIATELY CLBED BACK TO 10000 FT AND AT THE SAME TIME IAH APCH CTL WAS INSTRUCTING US TO CLB TO 10000 FT. AFTER REACHING 10000 FT I RECONNECTED THE AUTOPLT AND REPROGRAMMED THE FMC. THE FMC STARTED TO FUNCTION PROPERLY SO I REENGAGED IT. ALSO THE MCP PANEL WENT TO THE MASTER ARM ONLY TO MY SIDE WHICH IS THE PROPER FUNCTION IT SHOULD HAVE HAD. RESULT OF THE ABOVE: I DO NOT TRUST THE AUTO FUNCTION ON THE B-737 FOR I HAVE LEARNED THIS HAS HAPPENED TO OTHER CREWS. I'VE BEEN TOLD IT'S NOT SUPPOSED TO HAPPEN BUT IT DOES AND NO ONE KNOWS WHY. SUPPLEMENTAL INFO FROM ACN 295265: CONTRIBUTING FACTOR: I HAD BEEN ON OTHER RADIO GETTING ATIS AND CALLING COMPANY JUST PRIOR TO THIS EVENT. THEREFORE; AS I ENCOUNTERED THIS SIT; I HAD BEEN OUT OF 'THE LOOP' FOR SEVERAL MINS AND UNCERTAIN OF OUR CLRNC OR ANY CHANGES THERETO.