I resolved problem of sections on the page. And sidebar dropping down. That was of course matter of HTML ;).

It should look like this:

<p>content of 1st section<br />
<!–nextpage–><br />
content of 2nd section</p>
<p><!–nextpage–></p>
<p>content of 3rd section</p>
<p><!–nextpage–></p>
<p>content of 4th section </p> and so on…

The first section shouldn’t end with < /p >. So simple that I couldn’t figured it out at the beginning :).