ACR X AND ACR Y TCASII TA RA NON ADHERENCE TO ATC CLRNC STOPPED CLB AND DSCNT HAD LTSS. EVASIVE ACTION TAKEN.

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ACR X WAS ISSUED ALT OF 11000 (CLBING) AND ACR Y WAS DSNDING TO 8000. I WAS ANTICIPATING ACR X TO CLB ABOVE ACR Y. IT APPEARED THAT ACR X STOPPED THE CLB AT 9000 AND THAT THE ACR Y HAD STOPPED HIS DSCNT AT 10000. TFC WAS ISSUED AND THEN BOTH ACFT ADVISED THAT THEY HAD TCASII RA. ONLY ACR X HAD ANY TCASII INFO ON THE FLT STRIP. I WAS TAKING INTO CONSIDERATION BOTH ACFT PERFORMANCES AT THE TIME; AND THOUGHT THAT IT WAS NOT GOING TO BE A PROB. THE SECTOR I WAS WORKING WAS BUSY AND WE WERE TRYING TO OPEN ANOTHER RADAR SECTOR TO ALLEVIATE SOME OF THE TFC. BEING BUSY; I WAS UNABLE TO WATCH THE SIT AS IT DEVELOPED. BEING A LITTLE MORE CAUTIOUS IN ASSIGNING ALTS WILL BE ONE OF THE CONSIDERATIONS. BUT ALSO; WHEN TCASII IS INVOLVED; I'VE NOTICED THAT SOMETIMES THE PLT DECIDES WHETHER IT IS SAFE OR NOT TO CLB/DSND AND THAT CHANGES THE CTLR'S PLANS. SOMETIMES UNINTENTIONALLY. SUPPLEMENTAL INFO FROM ACN 226989: ACR X DURING CLB FROM ONT ON THE PRADO 2 DEP WE WERE CLRED TO 11000 FT. AS WE PASSED 9000 MSL; WE RECEIVED A TCASII TA FOLLOWED IMMEDIATELY BY AN RA COMMANDING A DSCNT OF AT LEAST 2000 FPM. AT ABOUT THE SAME TIME; THE DEP CTLR ASKED ACR Y IF HE WAS CLBING. THE CREW SAID THEY WERE RESPONDING TO AN RA AND HAD STOPPED THEIR DSCNT AND WERE LEVELING AT 10000. I WAS FLYING AND SAW ACR Y AND DSNDED FROM APPROX 9300 FT TO 9000 FT. THE FO CONFIRMED WE HAD BEEN CLRED TO 11000 AND WE ADVISED THE CTLR IN RESPONSE TO AN RA WE HAD STOPPED OUR CLB AND WERE LEVEL AT 9000. ACR Y ALSO CONFIRMED THAT HE HAD BEEN CLRED TO 8000. WHEN THE ACFT WERE CLR; WE EACH CONTINUED TO OUR ASSIGNED ALTS. THE CTLR SEEMED COMPLETELY UNCONCERNED. WE BELIEVE WE CAME WITHIN 700 FT AT 2.5 NM AND WOULD HAVE BEEN ON A POTENTIAL COLLISION COURSE IF BOTH CREWS HAD NOT RESPONDED TO THEIR TCASII. WE WERE ON A SOUTHEASTERLY COURSE AND ACR Y WAS APPROX W COURSE. THIS PUT HIM BEHIND MY L WINDOW POST AND PREVENTED AN EARLIER VISUAL SIGHTING.