my single.php is mixup on some post for no reason

I would check the post content of the post that is not shown well for unclosed or unopened <div>, <span>, whatever elements. If you are using Firefox, CMD+U (or Ctrl+U) will show you the source code that – for example – shows unopened but closed <a> and <p> tags in lines 853, 878… also w3c validation would be a good idea.

But, please… nothing happens “for no reason”… 😉