title: iOS UIButton disappears after setting background image to nil
body: <p>I have a UIButton that has no title or initial background image.  When pressed, the button background image changes and when pressed again, it is set to nil.  Now with iOS 6.x, the button completely disappears.  Here is my code:</p>
  
  <pre><code>- (IBAction)resetAll: (id) sender {
  [self reset];
  
  for (UIView *view in self.view.subviews) {
  
      if ([[[view class] description] isEqualToString:@"UIRoundedRectButton"]) {
          UIButton *theButton = (UIButton *)view;         
  
          int nTag = theButton.tag;
  
          switch (nTag) {
              case 11: {
                  theButton.tag = 10;
                  [theButton setBackgroundImage:nil forState:UIControlStateNormal];
                  break;
              }
              case 21: {
                  theButton.tag = 20;
                  [theButton setBackgroundImage:nil forState:UIControlStateNormal];
                  [theButton setEnabled:YES];
                  break;
              }
              case 31: {
                  theButton.tag = 30;
                  [theButton setBackgroundImage:nil forState:UIControlStateNormal];
                  [theButton setEnabled:YES];
                  break;
              }
              case 41: {
                  theButton.tag = 40;
                  [theButton setBackgroundImage:nil forState:UIControlStateNormal];
                  [theButton setEnabled:YES];
                  break;
              }
              case 51: {
                  theButton.tag = 50;
                  [theButton setBackgroundImage:nil forState:UIControlStateNormal];
                  [theButton setEnabled:YES];
                  break;
              }
          }
      }
  }
  return;
  </code></pre>
  
  <p>This code works fine:</p>
  
  <pre><code>- (IBAction)ButtonClicked: (id) sender {
  UIButton *btn = (UIButton *)sender;
  
  // Get the current tag value
  int currentTag = [sender tag];
  
  // Toggle the check buttons
  if (currentTag == 10 || currentTag == 20 || currentTag == 30 || currentTag == 40 || currentTag == 50) {
          [btn setBackgroundImage:[UIImage imageNamed:@"check.png"] forState:UIControlStateNormal];
          btn.tag = ++currentTag;
  }
  
  else
      if (currentTag == 11 || currentTag == 21 || currentTag == 31 || currentTag == 41 || currentTag == 51) {
          [btn setBackgroundImage:nil forState:UIControlStateNormal];
          btn.tag = --currentTag;
  }
  
  [self calculate];
  </code></pre>
  
  <p>Any suggestions or help would be appreciated!</p>