ACFT EQUIP PROB -- FLC COULD NOT GET THE ACFT ILS RECEIVER TO TUNE AND REMAIN TUNED TO THE LATEST ILS FREQ SO THE APCH CTLR ASSIGNED THEM THE ILS THAT IT WOULD TUNE.

Narrative

WHILE FLYING FLT BTWN EYW-MIA; MIA APCH INFORMED US WE WOULD BE LNDG TO THE W. COMING FROM THE SW WE ANTICIPATED RWY 30 OR RWY 27L. WE WERE THEN ADVISED TO EXPECT RWY 27L. WE WERE ALL SET UP FOR RWY 27L; THEN THE CTLR AT THE LAST MIN ADVISED WE COULD EXPECT RWY 27R. WE SET UP FOR RWY 27R. I THE PNF VERIFIED AND IDENTED THE 2 NAV RADIOS. THEY WERE SET TO 109.1 MIA RWY 27R. WE WERE THEN CLRED FOR THE APCH AND THE AUTOPLT QUICKLY COUPLED TO THE LOC. I LOOKED AT MY HSI WONDERING WHY IT COUPLED SO QUICKLY AND MY CDI SHOWED FULL R DEFLECTION. AT THAT MOMENT THE CTLR ADVISED US WE WERE TRACKING IN ON THE RWY 27L APCH. HE THEN SAID IF YOU WANT RWY 27L; NO PROB. FLY IT INBOUND AND CLRED US FOR THE APCH. THERE WAS NO OTHER TFC CLOSE TO US OR ON THE LOC RWY 27L; LUCKILY. AFTER LNDG AND WONDERING WHY THE R NAV RADIO WAS ON THE WRONG FREQ WE DEPRESSED THE FLIP FLOP BUTTON (FREQ CHANGE) AND DISCOVERED IT WOULD RETURN TO THE LAST ASSIGNED FREQ AFTER SEVERAL SECONDS. ALSO WHEN SELECTING A NEW FREQ AND PUSHING THE CHANGE BUTTON THE RADIO WOULD REVERT TO 110.0 FOR NO REASON. AFTER THE FLT THE RADIO WAS WRITTEN UP IN THE LOG AND REPLACED WITH ANOTHER UNIT. ALSO HAD ATC NOT CHANGED OUR RWY AT THE LAST MOMENT THIS WOULD NOT HAVE HAPPENED. MIA ALSO CHANGES DEP RWYS AT THE LAST SECOND. WE HAVE BEEN LINED UP ON RWY 9L AND THEN CLRED FOR TKOF ON RWY 12. THIS HAS HAPPENED 2 TIMES TO ME AND I HAVE HEARD MIA TWR DO IT TO OTHER AIRLINES. NOT GOOD.