I noticed broken file icons in the list / table view of my Plone 5.1 installation. I found that the icons are referenced with an absolute path there, which breaks my Apache Rewrite Rule. screenshot:
I took a few hours to get my head around the code. In my understanding the MimeTypeIcon function from plone.app.contentlisting doesn't work provide the absolute path for virtual environments.
I for one can't help you with your Apache rewrite rule - I use Ansible Plone that is only relying on Nginx. Whatever the reason, I have never seen your problem either with 5.1 or 5.1.2. When accessing directly (through 8080 port) the URL includes a 'Plone' (as it should be) and accessing through 80 or 443 port - through Nginx - there is no 'Plone' in the Url.
As you did not provide a screenshot of your broken display I am providing one in case I did not understand what you mean by 'broken icon' in tabular view, here is what I get: