Checkbox is invisible after deselecting in iOS

I am creating checkbox in iOS on PDF. But my checkbox is disappears after uncheking the checbox field.
I also tried to use custom appearance method from sample. But still same result. Can any one help me to resolve this.

Sample source code1 : using sample method.
Obj* CreateCheckmarkAppearance(PDFDoc *doc, enum CheckStyle style)
  // Create a checkmark appearance stream ------------------------------------
  ElementBuilder *build = [[ElementBuilder alloc] init];
  ElementWriter *writer = [[ElementWriter alloc] init];
    SDFDoc *s = [doc GetSDFDoc];
  [writer WriterBeginWithSDFDoc: s compress: YES];
  [writer WriteElement: [build CreateTextBegin]];
  NSString* symbol = @"\154";
  switch (style) {
    case e_circle: symbol = @"\154"; break;
    case e_diamond: symbol = @"\165"; break;
    case e_cross: symbol = @"\65"; break;
    case e_square: symbol = @"\156"; break;
    case e_star: symbol = @"\110"; break;
      // ...
      // See section D.4 "ZapfDingbats Set and Encoding" in PDF Reference Manual
      // ( for the complete
      // graphical map for ZapfDingbats font. Please note that all character codes
      // are represented using the 'octal' notation.
    default: // e_tick
      symbol = @"\64";
  Element *checkmark = [build CreateTextRunWithFont: symbol font: [Font Create: s type: e_zapf_dingbats embed: NO] font_sz: 1];
  [writer WriteElement: checkmark];
  [writer WriteElement: [build CreateTextEnd]];
  Obj *stm = [writer End];
  [stm PutRect: @"BBox" x1: -0.2 y1: -0.2 x2: 1 y2: 1]; // Clip
  [stm PutName: @"Subtype" name: @"Form"];
  return stm;

Sample Second : tField = [docToOpen FieldCreateWithString: @"Checkbox" type: e_check field_value: value def_field_value: @""];