We have a clean setup of Windows 2012 Standard, IIS 8, PHP and WinCache (installed from WPI). If you download and load the latest WordPress install (3.5) and then try to install a theme. It breaks.
Configuration is all standard with exception that the web server is accessing data via a share. The configuration allows the user to read and write from that configuration if you upload a simple PHP script that generates a random folder or file and writes data to it so permissions are good.
Can the IIS team please replicate and let us know?