MLG HAS TCASII RA TO DSND; THEN CHANGED TO CLB. CONFUSING.

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ON ARR INTO OKC APPROX 20 NM SSE OF IRW; WE WERE DSNDING THROUGH 6000 FT TO OUR CLRED ALT OF 4000 FT. PROCEEDING DIRECT TO GALLY OM FOR RWY 35R. THERE WERE NUMEROUS TARGETS ON TCASII 2000-3000 FT BELOW. APCH CTL CALLED TFC AT 12 O'CLOCK AND 5 MI 3500 FT. WE ALSO GOT A 'TFC; TFC' CALL (TA) FROM TCASII AND NOTED FROM TCASII THAT THE TFC WAS CLBING. BY THIS TIME WE WERE DSNDING THROUGH 4300 FT. THE CAPT DIRECTED ME TO CLB BACK TO 4500 FT. I ENGAGED ALT HOLD MODE OF THE AUTOPLT AT THAT TIME TO BREAK THE RATE OF DSCNT. AS THE CAPT ADVISED APCH CTL THAT WE WOULD BE CLBING BACK TO 4500 FT; APCH RECOMMENDED A 20 DEG R TURN IN ADDITION TO COINCIDE WITH THE CLB BACK TO 4500 FT. AS I WAS STARTING THE CLB WITH THE AUTOPLT IN VERT SPD MODE AND TURNING; TCASII ISSUED AN RA TO 'DSND; DSND.' WHILE CLICKING OFF THE AUTOPLT I NOTED THE GREEN ARC AT 2000 FPM DOWN; THE REST WAS RED. AT THIS TIME WE HAD ABOUT 500 FPM CLB. AS I STARTED TO BREAK THE CLB; THE TCASII CHANGED TO 'CLB; CLB' REQUESTING A 2000 FPM CLB WHICH I RESPONDED TO IN AN AGGRESSIVE MANNER. WHEN TCASII SOUNDED 'CLR OF CONFLICT' WE LEVELED OFF AT APPROX 5000 FT AND 20-30 DEGS R OF THE ORIGINAL HDG. MINIMUM OBSERVED VERT SEPARATION ON TCASII WAS 300 FT AND CTRED ON HORIZ DISPLAY. THERE WAS AN FAA ACR INSPECTOR ON THE JUMP SEAT. NO ONE IN THE COCKPIT SAW THE ACFT VISUALLY. VISIBILITY WAS UNRESTR BUT LOOKING DOWN THERE WAS A LIGHT SNOW COVERING ON THE GND; WITH DARK CONTRASTS FROM HOUSES; ETC; MAKING VISUAL ACQUISITION VERY DIFFICULT. THE TCASII REVERSING THE DIRECTION OF MANEUVER WAS A LITTLE CONFUSING AS OUR TRAINING IS TO NEVER MANEUVER IN THE DIRECTION OPPOSITE THAT CALLED FOR BY TCASII BECAUSE IT WOULD NEVER REVERSE (WHICH ACFT WOULD GO HIGH AND WHICH WOULD GO LOW) IN CASE IT WAS A COORDINATED MANEUVER BTWN 2 TCASII EQUIPPED ACFT. THIS CAUSED A SMALL HESITATION ON MY PART BEFORE CLBING ALTHOUGH BOTH THE CAPT AND FAA INSPECTOR STATED THAT THERE HAD BEEN NO DELAY IN INITIATING THE CLB. I WOULD LIKE TO SEE A CLARIFICATION ON WHEN TCASII WILL CHANGE ITS 'MIND' ON DIRECTION TO ELIMINATE THAT HESITATION IN THE FUTURE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES HE WISHES THE CTLR WOULD HAVE GIVEN THE VECTOR EARLIER THEN THE INCIDENT WOULD NOT HAVE OCCURRED. HE DID DISCUSS THIS WITHIN THE COMPANY BUT DOES NOT KNOW WHAT DEVELOPED. COMPANY HAD PUT OUT A NOTICE PREVIOUSLY THAT INDICATED IF ACFT IS CLBING AND TCASII INDICATES RA TO CLB; THE OTHER ACFT TCASII WILL DO EVERYTHING TO ASSURE IT GOES UNDER YOU. RPTR NOT SO SURE OF THIS; HOWEVER. HE DID COMPLY WITH TCASII INSTRUCTIONS AND THE PROB DID RESOLVE ITSELF WITH THE VECTOR ADDED. ACFT WAS AN MD88.