Program: 22583
Project: 22583
Buggy source:
/** 
 * Escapes a Unicode string to an all-ASCII character sequence. Any special characters are escaped using backslashes (<tt>"</tt> becomes <tt>\"</tt>, etc.), and non-ascii/non-printable characters are escaped using Unicode escapes (<tt>&#x5C;uxxxx</tt> and <tt>&#x5C;Uxxxxxxxx</tt>).
 * @throws IOException
 */
public static void escapeString(String label,Appendable appendable) throws IOException {
  int first=0;
  int last=label.length();
  if (last > 1 && label.charAt(0) == '<' && label.charAt(last - 1) == '>') {
    first++;
    last--;
  }
 else   if (label.charAt(0) == '"') {
    first=1;
    appendable.append('"');
    for (int i=last - 1; i > 0; i--) {
      char curr=label.charAt(i);
      if (curr == '"') {
        last=i;
        break;
      }
      char prev=label.charAt(i - 1);
      if (curr == '@' && prev == '"') {
        last=i - 2;
        break;
      }
      if (curr == '^' && prev == '^') {
        last=i - 2;
        break;
      }
    }
  }
  for (int i=first; i < last; i++) {
    char c=label.charAt(i);
    int cInt=c;
    if (c == '\\') {
      appendable.append("String_Node_Str");
    }
 else     if (c == '"') {
      appendable.append("String_Node_Str");
    }
 else     if (c == '\n') {
      appendable.append("String_Node_Str");
    }
 else     if (c == '\r') {
      appendable.append("String_Node_Str");
    }
 else     if (c == '\t') {
      appendable.append("String_Node_Str");
    }
 else     if (cInt >= 0x0 && cInt <= 0x8 || cInt == 0xB || cInt == 0xC || cInt >= 0xE && cInt <= 0x1F || cInt >= 0x7F && cInt <= 0xFFFF) {
      appendable.append("String_Node_Str");
      appendable.append(toHexString(cInt,4));
    }
 else     if (cInt >= 0x10000 && cInt <= 0x10FFFF) {
      appendable.append("String_Node_Str");
      appendable.append(toHexString(cInt,8));
    }
 else {
      appendable.append(c);
    }
  }
  appendable.append(label.subSequence(last,label.length()));
}

Fixed version (ground truth):
/** 
 * Escapes a Unicode string to an all-ASCII character sequence. Any special characters are escaped using backslashes (<tt>"</tt> becomes <tt>\"</tt>, etc.), and non-ascii/non-printable characters are escaped using Unicode escapes (<tt>&#x5C;uxxxx</tt> and <tt>&#x5C;Uxxxxxxxx</tt>).
 * @throws IOException
 */
public static void escapeString(String label,Appendable appendable) throws IOException {
  int first=0;
  int last=label.length();
  if (last > 1 && label.charAt(0) == '<' && label.charAt(last - 1) == '>') {
    first++;
    last--;
  }
 else   if (label.charAt(0) == '"') {
    first=1;
    appendable.append('"');
    for (int i=last - 1; i > 0; i--) {
      char curr=label.charAt(i);
      if (curr == '"') {
        last=i - 1;
        break;
      }
      char prev=label.charAt(i - 1);
      if (curr == '@' && prev == '"') {
        last=i - 2;
        break;
      }
      if (curr == '^' && prev == '^') {
        last=i - 3;
        break;
      }
    }
  }
  for (int i=first; i <= last; i++) {
    char c=label.charAt(i);
    int cInt=c;
    if (c == '\\') {
      appendable.append("String_Node_Str");
    }
 else     if (c == '"') {
      appendable.append("String_Node_Str");
    }
 else     if (c == '\n') {
      appendable.append("String_Node_Str");
    }
 else     if (c == '\r') {
      appendable.append("String_Node_Str");
    }
 else     if (c == '\t') {
      appendable.append("String_Node_Str");
    }
 else     if (cInt >= 0x0 && cInt <= 0x8 || cInt == 0xB || cInt == 0xC || cInt >= 0xE && cInt <= 0x1F || cInt >= 0x7F && cInt <= 0xFFFF) {
      appendable.append("String_Node_Str");
      appendable.append(toHexString(cInt,4));
    }
 else     if (cInt >= 0x10000 && cInt <= 0x10FFFF) {
      appendable.append("String_Node_Str");
      appendable.append(toHexString(cInt,8));
    }
 else {
      appendable.append(c);
    }
  }
  appendable.append(label.subSequence(last + 1,label.length()));
}