MLG FLC HAS TCASII TA. LOOKING OUTSIDE; THEY NEGLECT TO LEVEL OFF. ALT ALERT GOES OFF; RETURN TO ASSIGNED.

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WHILE DSNDING TO 7000 FT; OUR CLRED ALT; AT ABOUT 7200 FT WE GOT A 'TA' FROM THE TCASII. I OBSERVED A TARGET ON THE TCASII SCREEN AT 12 O'CLOCK AND QUITE CLOSE. I T HAD NO ALT RPTING. BOTH PLTS IMMEDIATELY BEGAN SEARCHING OUTSIDE FOR THE TFC. SUDDENLY; THE 'ALT ALERT' WENT OFF. WE HAD GONE THROUGH 7000 FT WHILE LOOKING FOR THE TFC. WE LEVELED OFF ABOUT 250 FT BELOW 7000 FT AND CLBED BACK TO 7000 FT. AT THE SAME TIME; I LOOKED AT THE TCASII SCREEN AND THE 'TA' TARGET WAS GONE. IT IS ALMOST IMPOSSIBLE FOR A PLT TO NOT SEARCH OUTSIDE FOR A 'TA' FROM TCASII. EVEN THOUGH YOU HAVE BEEN WATCHING FOR TFC; THIS CAN CAUSE A DISTR FROM FLYING THE AIRPLANE. I HAVE NOTICED THAT AT TIMES; TCASII TARGETS SUDDENLY APPEAR AND DISAPPEAR. MAYBE CAUSED BY THE AIRFRAME BLANKING TRANSPONDER SIGNALS FROM CERTAIN ANGLES. THE TARGET IN THIS RPT SUDDENLY APPEARED; CAUSED A 'TA' AND DISTRACTED THE CREW JUST AS WE SHOULD HAVE BEEN LEVELING OFF. I DON'T KNOW THE ANSWER TO THE PROBLEM OF POSSIBLE DISTRS CAUSED BY TCASII. IT CAN BE A PROBLEM AND SEEMS TO BE A NORMAL HUMAN REACTION TO A WARNING. I HAVE OVER 1 YR OF EXPERIENCE FLYING WITH TCASII INSTALLED IN MY AIRPLANE. THIS SPECIFIC TFC WAS NEVER SIGHTED VISUALLY. SUPPLEMENTAL INFO FROM ACN 215432: I BELIEVE THE ADVANTAGES OF TCASII FAR OUTWEIGH THE DISTR IT CAN OCCASIONALLY CAUSE.