Jquery mobile 1.3 navbar hide content

Jquery mobile 1.3 navbar hide content

Hi,
i have this problem.
I have an application with a persistent navbar.
When i charge the main page for the first time, the top of content is hide by navbar. If a navigate to app, when i return in main page, the content is ok.
This is the code of first page.

<div data-role="page" id="pg_main" data-ajax="true" >
<div data-role="panel" data-id="main_panel" id="main_panel" class="main_panelcolor" data-position="left" data-inline="true" data-display="overlay" data-position-fixed="true" data-dismissible="true" >
        <ul data-role="listview" data-theme="a" id="main_list">
        <li><a href="#pg_main"><img src="img/home.png" class="ui-li-icon">Home</a></li>
        <li><a href="#pg_regioni"><img src="img/ciao.png" class="ui-li-icon">Ciao</a></li>
        <li><a href="#pg_stampa" class="stampapannello"><img src="img/stampa.png" class="ui-li-icon">Stampa</a></li>
        <li><a href="#pg_contatti"><img src="img/contatti.png" class="ui-li-icon">Contatti</a></li>
        <li><a class="btn_facebook"><img src="img/social.png" class="ui-li-icon">Social</a></li>
        <li><a href="#pg_video"><img src="img/video.png" class="ui-li-icon">Video</a></li>
        <li><a href="#pg_informazioni"><img src="img/info.png" class="ui-li-icon">Informazioni</a></li>
        </ul>
        </div> 
<div data-role="header" data-id="main_header"  data-theme="b" data-position="fixed">
<img class="logo_main" src="img/logomain.PNG"/>
<a href="#main_panel" data-role="button" id="btn_altreazioni" data-icon="bars"   data-iconpos="notext"></a>
<div data-role="navbar" >
<ul>
<li><a href="#pg_main" class="ui-btn-hover-b">Home</a></li>
<li><a href="#pg_main1" data-transition="slide">Chi siamo</a></li>
<li><a href="#pg_main2" data-transition="slide">Galleria</a></li>
</ul>
</div>
</div>
<!-- /navbar -->
<!-- /header -->
<div  id="div_main_img" data-role="content" >
<img id="main_img" src="img/desktop.jpg"></img>
</div><!-- /content -->
</div>
 
Thanks a lot.