title: UITextField placeholder text overlay issue
body: <p>I have a table view with three table view cells.
  During cell configuration, I add a UITextField to each of the cells and I also set the placeholder value on all of the text fields.
  When the table view loads the end results looks like this:</p>
  
  <p><img src="https://i.stack.imgur.com/QjjD6.png" alt="Table view after load"></p>
  
  <p>The issue I'm having, is that when I scroll any of the cells "off the screen" when they reappear the placeholder text get darker and darker, like here:</p>
  
  <p><img src="https://i.stack.imgur.com/PKNSJ.png" alt="Darker placeholder text"></p>
  
  <p>When I then attempt to change the UITextField string value by typing a name in, or by programatically changing the placeholder value on the last cell, the old value of those properties stays, and the new value gets overlaid in the cell, like this:</p>
  
  <p><img src="https://i.stack.imgur.com/ij21l.png" alt="enter image description here"></p>
  
  <p>Here are the methods responsible for configuring those cells:</p>
  
  <pre><code>- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
  {
      static NSString *CellIdentifier = @"Cell";
      UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
  
      // Configure the cell...
      [self configureCell:cell forIndexPath:indexPath];
  
      return cell;
  }
  
  - (void)configureCell:(UITableViewCell *)cell forIndexPath:(NSIndexPath *)indexPath
  {
      for (UIView *subview in cell.contentView.subviews) {
          [subview removeFromSuperview];
      }
  
      cell.backgroundColor = [UIColor whiteColor];
      cell.autoresizesSubviews = YES;
      cell.clearsContextBeforeDrawing = YES;
      CGRect textFieldFrame = cell.bounds;
      textFieldFrame.origin.x += 10;
      textFieldFrame.size.width -= 10;
  
      UITextField *textField = [[UITextField alloc] initWithFrame:textFieldFrame];
      textField.adjustsFontSizeToFitWidth = YES;
      textField.textColor = [UIColor lightGrayColor];
      textField.enabled = YES;
      textField.userInteractionEnabled = NO;
      textField.autoresizingMask = UIViewAutoresizingFlexibleWidth;
      textField.clearsContextBeforeDrawing = YES;
      textField.clearsOnBeginEditing = YES;
  
      if (indexPath.section == ATTAddNewTimerSectionName) {
          textField.placeholder = @"Name";
          textField.userInteractionEnabled = YES;
          textField.delegate = self;
          textField.returnKeyType = UIReturnKeyDone;
          textField.clearButtonMode = UITextFieldViewModeWhileEditing;
      } else if (indexPath.section == ATTAddNewTimerSectionDate) {
          textField.placeholder = @"Date/Time";
          cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
      } else if (indexPath.section == ATTAddNewTimerSectionCalendar) {
          if (self.userCalendarEvent == nil) {
              textField.placeholder = @"See list of calendar events";
          } else {
              textField.placeholder = nil;
              textField.placeholder = self.userCalendarEvent.title;
          }
          cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
      }
      [cell addSubview:textField];
  }
  </code></pre>
  
  <p>As you can see, I have tried various things, like removing all the subviews before adding a new view to the cell or setting -[UIView setClearsContextBeforeDrawing:YES] on both the cell and the UITextView and even setting the placeholder value to nil without success.</p>
  
  <p>Any pointers would be much appreciated!</p>