AN ACR MLG DSNDED IN RESPONSE TO A SERIES OF CONFUSING TCASII COMMANDS.

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VFR ACFT WAS TOLD BY APCH CTL TO REMAIN AT 5500 FT. WE WERE HOLDING ON APCH COURSE AT OM AT 4000 FT. ANOTHER ACFT (HELI) WAS HOLDING AT 3000 FT MSL. AFTER RECEIVING A 'DSND' COMMAND ON OUR TCASII; WE INITIATED A DSCNT FROM OUR HOLDING ALT. AFTER DSNDING APPROX 300 FT; WE OBSERVED WHAT APPEARED TO BE AN SMA IN A STEEP DIVE THROUGH THE CLOUDS APPROX 1/4 MI AHEAD AND 100-200 FT BELOW US. ATC WAS IN CONTACT WITH THIS ACFT AND THERE WAS A RADIO EXCHANGE BTWN THE ACFT AND BFL APCH CTL. ACFT COULD NOT HAVE MAINTAINED BASIC CLOUD CLRNC. THE MANEUVER WE OBSERVED COULD ONLY HAVE BEEN A DIVE TO AVOID US OR AN ATTEMPT TO DIVE THROUGH A HOLE IN THE CLOUDS TO VFR. SUPPLEMENTAL INFO FROM ACN 236178: WE BRIEFLY SAW A SMALL HIGH WING SMA IN A VERY STEEP DIVE WHICH HAD MOVED FROM OUR R TO L. AFTER CONVERSATIONS WITH TWR PERSONNEL; WE WERE ABLE TO ASCERTAIN THAT THE ACFT WAS VFR ONLY AND WAS TOLD TO REMAIN VFR AND CLR OF OUR POS. IN OUR PROFESSIONAL OPINION; HE WAS NOT IN VFR CONDITIONS. VFR FLT RULES AS DEFINED WOULD MAKE HIM ABSOLUTELY OPERATING ILLEGALLY AND IN AN IFR ENVIRONMENT. WE BELIEVE THIS INCIDENT OCCURRED DUE TO BAD JUDGEMENT ON THE VFR ACFT'S PART; AND IN HIS NOT STAYING VFR AND OBEYING THE CTLR. WHY WX WAS NOT MORE ACCURATE COULD HAVE BEEN A FACTOR FOR HIM AS WELL.