ACR WDB ALT DEV EXCURSION FROM CLRNC ALT IN RESPONSE TO TCASII RA. TRACON SUPVR QUESTIONS THE DEV IN VIEW OF THE FACT THAT A TA HAD BEEN GIVEN.

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WE WERE BEING VECTORED FOR CLB FROM EWR ENRTE TO LAX. PASSING 7800 FT WE WERE TOLD TO LEVEL AT 8000 FT 'IF ABLE'. I LEVELED AT 8070 FT. ATC ISSUED A TA AT '11 O'CLOCK; 4 MI; 8500 FT'. A LOOKED IN THAT DIRECTION; AND SAW AN ACFT MOMENTARILY. AT THE SAME TIME MY FO CALLED 'TCASII TA'. I LOOKED BACK INSIDE AND HE IMMEDIATELY CALLED 'RA'. I DISCONNECTED THE AUTOPLT; LOOKED AT THE VERT SPD INDICATOR AND REALIZED THAT IT WAS COMMANDING ME TO DSND AT APPROX 1500 FPM. I PUSHED THE NOSE OVER TO COMPLY. UPON REACHING APPROX 7800 FT THE RA DISAPPEARED. MY FO ADVISED ATC THAT WE HAD A TCASII RA AND WERE COMPLYING WITH IT. ANOTHER CTLR CAME ON FREQ AND QUESTIONED US AS TO WHY WE HAD COMPLIED WITH THE RA WHEN THE TFC HAD BEEN RPTED TO US AND THAT THERE WAS OTHER TFC BELOW US. I HAD SEEN AN ACFT FOR 1-2 SECONDS. I DID NOT CALL IT IN SIGHT AND DID NOT KNOW IF IT WAS THE TFC CAUSING THE CONFLICT. SINCE I NO LONGER HAD VISUAL CONTACT; I FOLLOWED THE TCASII INSTRUCTIONS. I FELT THAT THE CTLR DID NOT UNDERSTAND MY OBLIGATION IN THIS SITUATION AS COMPARED TO A TCASII TA.