To close up the issue for anyone having it in the future:
The problem was IIS stripping out the data and not passing that onto the underlying modules correctly.
This can be due to incorrect setups, alternative modules overriding your configurations and possibly many more things.
To resolve the issue, I had to entirely uninstall IIS and WPAS (Windows Process activation service) from the "Control Panel" -> "Programs and Features" -> "Activate/Deactivate Windows Features"
(
NOTE: This will entirely wipe your IIS configurations and any existing websites or webservices that you have running! Backup before you continue! Always backup!)
I also renamed/deleted the IIS folders "C:\inetpub" and "C:\Windows\System32\inetsrv"
Then reinstall IIS and WPAS and resetup the CodeSite dispatchers in IIS.
After those steps, the HTTP dispatchers worked as intended.
Additional reading for those interested:
Link supplied by Ray regarding the potential issue:
http://stackoverflow.com/questions/3811300/delphi-native-web-service-applications-not-working-iis-7-seems-to-be-strippingRestoring IIS defaults and Backing up/Restoring IIS settings and defaults:
http://www.iis.net/learn/manage/managing-your-configuration-settings/using-configuration-history-with-iis-7-and-iis-8http://forums.iis.net/t/1207403.aspx?Restore+IIS+8+original+Default+Settingshttp://blogs.iis.net/bills/archive/2008/03/24/how-to-backup-restore-iis7-configuration.aspxhttp://forums.iis.net/t/1085990.aspx