Program: 11774
Project: 11774
Buggy source:
@Override public void manipulate(int relX,int y,int relZ,Substance substance,byte data){
  if (relX >= 0 && relX <= 15 && relZ >= 0 && relZ <= 15) {
    setAt(relX,y,relZ,substance,data,(byte)255,(byte)15);
    return;
  }
  int cx=location.x();
  int cz=location.z();
  int xMinDiff=Math.max(relX,0) - Math.min(relX,0);
  int xMaxDiff=Math.max(relX,15) - Math.min(relX,15);
  int zMinDiff=Math.max(relZ,0) - Math.min(relZ,0);
  int zMaxDiff=Math.max(relZ,15) - Math.min(relZ,15);
  if (relX < 0 && relZ > 15) {
    ChunkLocation loc=ChunkLocation.create(cx - up(xMinDiff / 16),cz + up(zMaxDiff / 16));
    TridentChunk chunk=rawChunk(loc);
    TridentLogger.get().debug(relX + "String_Node_Str" + relZ+ "String_Node_Str"+ xMinDiff+ "String_Node_Str"+ xMaxDiff+ "String_Node_Str"+ zMinDiff+ "String_Node_Str"+ zMaxDiff+ "String_Node_Str"+ (16 - xMinDiff)+ "String_Node_Str"+ (zMaxDiff - 1));
    chunk.setAndSend(16 - xMinDiff,y,zMaxDiff - 1,substance,data,(byte)255,(byte)15,change);
  }
 else   if (relX > 15 && relZ > 15) {
    ChunkLocation loc=ChunkLocation.create(cx + up(xMaxDiff / 16),cz + up(zMaxDiff / 16));
    TridentLogger.get().debug(relX + "String_Node_Str" + relZ+ "String_Node_Str"+ xMinDiff+ "String_Node_Str"+ xMaxDiff+ "String_Node_Str"+ zMinDiff+ "String_Node_Str"+ zMaxDiff+ "String_Node_Str"+ (xMaxDiff - 1)+ "String_Node_Str"+ (zMaxDiff - 1));
    TridentChunk chunk=rawChunk(loc);
    chunk.setAndSend(xMaxDiff - 1,y,zMaxDiff - 1,substance,data,(byte)255,(byte)15,change);
  }
 else   if (relX < 0 && relZ < 0) {
    ChunkLocation loc=ChunkLocation.create(cx - up(xMinDiff / 16),cz - up(zMinDiff / 16));
    TridentLogger.get().debug(relX + "String_Node_Str" + relZ+ "String_Node_Str"+ xMinDiff+ "String_Node_Str"+ xMaxDiff+ "String_Node_Str"+ zMinDiff+ "String_Node_Str"+ zMaxDiff+ "String_Node_Str"+ (16 - xMinDiff)+ "String_Node_Str"+ (16 - zMinDiff));
    TridentChunk chunk=rawChunk(loc);
    chunk.setAndSend(16 - xMinDiff,y,16 - zMinDiff,substance,data,(byte)255,(byte)15,change);
  }
 else   if (relX > 15 && relZ < 0) {
    ChunkLocation loc=ChunkLocation.create(cx + up(xMaxDiff / 16),cz - up(zMinDiff / 16));
    TridentLogger.get().debug(relX + "String_Node_Str" + relZ+ "String_Node_Str"+ xMinDiff+ "String_Node_Str"+ xMaxDiff+ "String_Node_Str"+ zMinDiff+ "String_Node_Str"+ zMaxDiff+ "String_Node_Str"+ (xMaxDiff - 1)+ "String_Node_Str"+ (16 - zMinDiff));
    TridentChunk chunk=rawChunk(loc);
    chunk.setAndSend(xMaxDiff - 1,y,16 - zMinDiff,substance,data,(byte)255,(byte)15,change);
  }
}

Fixed version (ground truth):
@Override public void manipulate(int relX,int y,int relZ,Substance substance,byte data){
  if (relX >= 0 && relX <= 15 && relZ >= 0 && relZ <= 15) {
    setAt(relX,y,relZ,substance,data,(byte)255,(byte)15);
    return;
  }
  int cx=location.x();
  int cz=location.z();
  int xMinDiff=Math.max(relX,0) - Math.min(relX,0);
  int xMaxDiff=Math.max(relX,15) - Math.min(relX,15);
  int zMinDiff=Math.max(relZ,0) - Math.min(relZ,0);
  int zMaxDiff=Math.max(relZ,15) - Math.min(relZ,15);
  int chunkX=location.x();
  int chunkZ=location.z();
  int newX=relX;
  int newZ=relZ;
  if (relX < 0) {
    newX=16 - xMinDiff;
    chunkX=cx - up(xMinDiff / 16) - 1;
  }
 else   if (relX > 15) {
    newX=xMaxDiff - 1;
    chunkX=cx + up(xMaxDiff / 16) + 1;
  }
  if (relZ < 0) {
    newZ=16 - zMinDiff;
    chunkZ=cz - up(zMinDiff / 16) - 1;
  }
 else   if (relZ > 15) {
    newZ=zMaxDiff - 1;
    chunkZ=cz + up(zMaxDiff / 16) + 1;
  }
  ChunkLocation loc=ChunkLocation.create(chunkX,chunkZ);
  TridentChunk chunk=rawChunk(loc);
  TridentLogger.get().debug(relX + "String_Node_Str" + relZ+ "String_Node_Str"+ xMinDiff+ "String_Node_Str"+ xMaxDiff+ "String_Node_Str"+ zMinDiff+ "String_Node_Str"+ zMaxDiff+ "String_Node_Str"+ newX+ "String_Node_Str"+ newZ);
  chunk.setAndSend(newX,y,newZ,substance,data,(byte)255,(byte)15,change);
}