A couple problems I noticed

Hello, unfortunately there are much more bugs! I’ve try to solve all in once within this release, but still remain one about logout that i will try to solve in this moments, hope this will not take too much time.
The problem, on iframe mode, is about logout user: it seem session isn’t properly set about cookie in the logout procedure in some particular circumstance, i will try to reverse to understand what going on. I think it affect only domain/subdomains installs.

About your problem: are you in iframe mode with javascript resizer or with a default css iframe as install setup for the forum page?

If you have not add the code about javascript responsive iframe, and css is the resizer of the iframe, it is a normal behavior because when content inside iframe change, the iframe do not modify his dimension.
Unique solution to this bad situation is to give by default sufficient space to the iframe. It is bad solution. To add/reduce space for the iframe with css not responsive, simply increase or decrease values on forum-template page, at the css line:
padding-bottom: 70.25%; /* proportion value to aspect ratio 16:9 (9 / 16 = 0.5625 or 56.25%) */
If you instead, have add modifications to the javascript code library included adding it (it is not still included elsewhere by default) but that i have not still documented how to install in minutes, please let me know and see what and how, so we can in case set it up improving all. I’m sure, it will be perfect as soon!

to get the page with sidebar as you want, the code of the page template that embed the iframe forum should be like this:

<?php
/**
 * The default basic template to display content for WP_w3all integration plugin
 * @package WordPress
 * @subpackage wp_w3all
 */
// START DO NOT MODIFY
if( preg_match('/[^0-9]/',$_GET["forum_id"]) OR preg_match('/[^0-9]/',$_GET["post_id"])){

	unset($_GET);
} 

$w3all_url_to_cms  = get_option( 'w3all_url_to_cms' );

  if (isset($_GET["forum_id"])){
    $uapp = "/viewtopic.php?f=".$_GET["forum_id"]."&p=".$_GET["post_id"]."#p".$_GET["post_id"]."";
    $w3all_url_to_cms = $w3all_url_to_cms . $uapp;
  } 

  add_action('wp_head','wp_w3all_hook_css');

/* WoW! this CSS work: http://www.bymichaellancaster.com/blog/fluid-iframe-and-images-without-javascript-plugins/ */
/* But it can't be responsive when iframe content change */

function wp_w3all_hook_css() {
	$w3all_css_ioutput="<style type=\"text/css\">.fluid_iframe {
    position: relative;
    padding-bottom: 86.25%; /* proportion value to aspect ratio 16:9 (9 / 16 = 0.5625 or 56.25%) */
    padding-top:0px;
    height: 0;
    overflow: hidden;
    background:#F5F7FA url(" . get_template_directory_uri() . '/'."inc/bgtop.png);
    background-position:top;
    background-repeat:repeat-x;
}

.fluid_iframe iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}

</style>";

	echo $w3all_css_ioutput;

}
// END DO NOT MODIFY

// Start a default WordPress page
get_header(); ?>

<div id="primary" class="content-area">
	<main id="main" class="site-main" role="main">
		<div class="fluid_iframe">
<iframe src="<?php echo $w3all_url_to_cms ?>" style="width:100%;border:0px;"
scrolling="no"
marginheight="0"
marginwidth="0">
   <p>Your browser does not support iframes. You can <a href="<?php echo get_option( 'w3all_url_to_cms' ) ?>">load full forum page here.</a></p>
</iframe>
</div>

	</main><!-- .site-main -->

	<?php get_sidebar( 'content-bottom' ); ?>

</div><!-- .content-area -->

<?php get_sidebar(); ?>
<?php get_footer(); ?>

http://www.originalgangster.eu/www-common/w3all_sidebar_template.jpg

NOTE that the above page code is ok for 1.0.6 version, DO NOT USE ON 1.0.7. 1.0.7 fix a bug about template page creation and add features.
Within little time 1.0.8 with iframe responsive ready will be available.