EAccessViolation mit Codeoptimierung

[turboPASCAL]

Delphi-Quellcode:

type
  FSOUND_SAMPLE = record

    buff: Punsignedchar;                // pointer to sound data
    ...
  end;
  PFSOUND_SAMPLE = ^FSOUND_SAMPLE;

  FSOUND_CHANNEL = record
    index: int;                         // position in channel pool.
    volume: int;                        // current volume (00-FFh).
    frequency: int;                     // speed or rate of playback in hz.
    pan: int;                           // panning value (00-FFh).
    actualvolume: int;                  // driver level current volume.
    actualpan: int;                     // driver level panning value.
    sampleoffset: unsignedint;          // sample offset (sample starts playing from here).

    sptr: PFSOUND_SAMPLE;               // currently playing sample

    ...
  end;

  PFSOUND_CHANNEL = ^FSOUND_CHANNEL;


procedure...
...
  asm
        push   ebp
        mov   ebx, mix_mixptr
        mov   mix_mixbuffptr, ebx

        mov   ecx, cptr
        mov   mix_cptr, ecx

        cmp   ecx, 0                         // if (!cptr) ...
        je   @MixExit                       //   ... then skip this channel!

>>>-->  mov   ebx, [ecx+FSOUND_CHANNEL.sptr] // load the correct SAMPLE pointer
                                               // for this channel

        mov   mix_sptr, ebx                  // store sample pointer away
        cmp   ebx, 0                         // if (!sptr) ...
        je   @MixExit                       //   ... then skip this channel!

        // get pointer to sample buffer
        mov   eax, [ebx+FSOUND_SAMPLE.buff]
        mov   mix_samplebuff, eax
...

Wieso kommt hier eine EAccessViolation ? Wenn ich in den Optionen vom Compiler die Codeoptimierung abschalte {$O-} gibt es keine Probleme.