I don't knok if it is the right way, but I tried to delete these lines in "main.php"
<div id="gkMainbody" class="gkMain <?php echo $this->generatePadding('gkMainbody'); ?>">
<?php if($this->modules('breadcrumb') || $this->getToolsOverride()) : ?>
<div id="gkBreadcrumb">
<div>
<div>
<div id="gkComponent">
<div>
<jdoc:include type="component" />
</div>
</div>
<?php elseif($this->getParam('mainbody_frontpage', 'only_component') == 'only_mainbody') : ?>
<jdoc:include type="modules" name="mainbody" style="<?php echo $this->module_styles['mainbody']; ?>" />
<?php elseif($this->getParam('mainbody_frontpage', 'only_component') == 'mainbody_before_component') : ?>
<jdoc:include type="modules" name="mainbody" style="<?php echo $this->module_styles['mainbody']; ?>" />
<div id="gkComponent">
<div>
<jdoc:include type="component" />
</div>
</div>
<?php else : ?>
<div id="gkComponent">
<div>
<jdoc:include type="component" />
</div>
</div>
<jdoc:include type="modules" name="mainbody" style="<?php echo $this->module_styles['mainbody']; ?>" />
<?php endif; ?>
<?php else : ?>
<?php if($this->getParam('mainbody_subpage', 'only_component') == 'only_component') : ?>
<div id="gkComponent">
<div>
<jdoc:include type="component" />
</div>
</div>
<?php elseif($this->getParam('mainbody_subpage', 'only_component') == 'mainbody_before_component') : ?>
<jdoc:include type="modules" name="mainbody" style="<?php echo $this->module_styles['mainbody']; ?>" />
<div id="gkComponent">
<div>
<jdoc:include type="component" />
</div>
</div>
<?php else : ?>
<div id="gkComponent">
<div>
<jdoc:include type="component" />
</div>
</div>
<jdoc:include type="modules" name="mainbody" style="<?php echo $this->module_styles['mainbody']; ?>" />
<?php endif; ?>
<?php endif; ?>
</div>And now it works. There are no more the ghost module.