ACR X HAD LTSS FROM ACR Y AT WRONG ALT. SYS ERROR PLTDEV.

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ACR X INBOUND TO TPA FROM THE (CAPT FLYING) WE HEARD TPA APCH AND AN ACR Y MD-80 ARGUING. IT SEEMED THAT Y WAS DEVIATING AROUND SOME TSTMS AT 3000 FT AND HAD NOT TOLD ATC OF SUCH HDG CHANGES. ATC WAS NOT PLEASED WITH THIS AND ASKED Y WHAT HE WAS DOING IN A SOMEWHAT HOSTILE COMMENT. I GUESS Y DID NOT LIKE ATC'S ATTITUDE ABOUT THE SIT AND SO THEY KEPT SAYING COMMENTS TO EACH OTHER. THEY THEN GOT IN TO IT ABOUT THE ALT THAT Y WAS SUPPOSED TO BE AT. ATC SAID 4000 FT AND Y SAID 3000 FT. WHILE ALL THIS WAS GOING ON; WE WERE CRUISING EBOUND ON RADAR VECTORS FOR RWY 18R IN TPA (LEVEL AT 3000 FT) AT ABOUT 3-4 MINS INTO ATC'S AND Y'S VERBAL FIGHT OVER THE AIR; ATC MUST HAVE REALIZED THAT THIS SIT WAS GETTING OUT OF HAND BECAUSE HE NOW HAD US HDG E AT 3000 FT AND Y HDG NW AT 3000 FT ON CONVERGING COURSES. ATC THEN POINTED TFC TO US AND PUT US ON A 330 HDG. WE GOT VISUAL ON Y AS WE STARTED THE TURN; I (FLYING THE ACFT) LOST SIGHT OF THE MD-80 UNDER THE R SIDE OF THE NOSE AS I BANKED AWAY FROM THEM. AT THIS POINT; ATC AGAIN TOLD THAT HE WAS SUPPOSED TO BE AT 4000 FT. WHILE WE WERE IN THE TURN MY FO SAID THAT THE MD-80 WAS STILL HDG FOR US. AT THIS POINT; I THOUGHT OF SEVERAL THINGS THAT I COULD DO: 1) ROLL WINGS LEVEL TO KEEP VISUAL ON THE MD-80. 2) CLB. 3) DSND; OR 4) KEEP TURNING TO THE NW. I CHOSE TO KEEP TURNING. IF I HAD ROLLED WINGS LEVEL; I WOULD HAVE PUT US CLOSER. I DID NOT WANT TO CLB OR DSND BECAUSE HE MIGHT HAVE DONE THE SAME. AS IT TURNED OUT; HE DSNDED UNDER. ALSO; WE HAD TCASII ON BOARD AND ALL IT SAID WAS TFC -- NO RA! IT WAS OBVIOUS THAT THIS WAS THE CAUSE OF THE ARGUMENT AND NEITHER Y OR ATC WAS DOING WHAT THEY WERE SUPPOSED TO BE DOING (FLYING OR SEPARATING TFC). Y WAS AT THE WRONG ALT AND ATC ALLOWED US TO GET TOO CLOSE.