Why does my Apache proxy request redirect to the wrong host on first request

Question

I'm using Apache to serve some html and JavaScript files in my /Apps folder and I'm using to proxy the rest of the requests to another web server running on the same system via ProxyPass.

Here's an example from my conf:

<VirtualHost *:80>
  ProxyPreserveHost On
  ProxyPass "/Apps" !
  ProxyPass "/" "http://localhost:8080/"
  ProxyPassReverse "/" "http://localhost:8080/"
</VirtualHost>

This is working as intended in most cases but on the first attempt to load the /Apps page on a fresh web browser it always adds the port of the secondary server into the URL which leads to an error. Why does this happen on the first attempt and how can I fix that?