A80 CTLR DESCRIBED PLTDEV EVENT WHEN ACR FAILED TO COMPLY WITH ALT RESTRICTIONS AFTER RWY CHANGE ASSIGNMENT.

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ACR X AT 45 DME FROM ATL; CHKED IN AT 14000 FT AND WAS INSTRUCTED 'RWY 28; DSND VIA THE HONIE5 ARR.' AT 41 DME FROM ATL; TMC CHANGED THE ASSIGNED RWY FOR ACR X TO RWY 26R. AT 37 DME FROM ATL; I INSTRUCTED ACR X; 'CHANGE TRANSITION AND RWY TO RWY 26R; MAINTAIN 14000 FT.' ACR X APPEARED TO HAVE STARTED A DSCNT ALREADY AND THE MODE C INDICATED 13700 FT; SO I INSTRUCTED; 'ACR X NO PROB IF YOU STARTED DOWN ALREADY; JUST CLB AND MAINTAIN 14000 FT. ACR X CONTACT ATL APCH CTL 128.0.' ALL THESE INSTRUCTIONS WERE ACKNOWLEDGED. AT 32 DME FROM ATL; I NOTICED THAT ACR X MODE C INDICATED 15000 FT. I CALLED ZTL TIROE SECTOR AND ADVISED THAT ACR X HAD APPARENTLY CLBED TO 15000 FT AND THAT HE WAS DSNDING AGAIN. I THEN EFFECTED COORD WITH ANOTHER CTLR TO TELL ACR X TO DSND TO 14000 FT. ACR X WAS NOT ON HIS FREQ YET; SO I BROADCAST FOR ACR X. ACR X ASKED ME 'WHAT WAS THAT FREQ?' I INSTRUCTED ACR X TO MAINTAIN 14000 FT AND CONTACT APCH 128.0. AT 25 DME; ACR X RETURNED AND ASKED ME THE FREQ AGAIN. THE PLT CALLED VIA TELEPHONE AND SAID THAT WHEN HE ENTERED THE NEW TRANSITION; THE RNAV DROPPED OUT OF THE BOX.