Thanks for other answers here. I found out what causes the bug.
- (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath
{
[cell setBackgroundColor:[UIColor clearColor]];
}
Here it is the bug described which is in iOS 7 versions. https://stackoverflow.com/a/18878259/1083859