Ribbon and scrollbar in 2013

Hi,

I'm using SecurityTrimmedControl on my masterpage to hide the ribbon from everyone except administrators (code below). A side effect is that this also seems to hide the scrollbar and list dialogs no longer renders properly.

I've been searching for a solution, and it seems this also occurred in 2010 but I've not found an easy solution for 2013. Any ideas?

<div class="ms-belltown-anonShow">
                 <!--MS:<SharePoint:SPSecurityTrimmedControl PermissionsString="FullMask" runat="server">-->
                <div id="ms-designer-ribbon">
                    <!--SID:02 {Ribbon}-->
                    <!--PS: Start of READ-ONLY PREVIEW (do not modify) --><div class="DefaultContentBlock" style="background:rgb(0, 114, 198); color:white; width:100%; padding:8px; height:64px; overflow:hidden;">In true previews of your site, the SharePoint ribbon will be here.</div><!--PE: End of READ-ONLY PREVIEW -->
                </div>
                 <!--ME:</SharePoint:SPSecurityTrimmedControl>-->
                <!--MS:<SharePoint:SPSecurityTrimmedControl runat="server" AuthenticationRestrictions="AnonymousUsersOnly">-->
                    <!--SPM:<wssucw:Welcome runat="server" EnableViewState="false"/>-->
                <!--ME:</SharePoint:SPSecurityTrimmedControl>-->
            </div>