Steps to reproduce:
  1. Install mod_security on Windows Server 2008 R2 x64, IIS 7.5 using msi installer
  2. Setup mod_security for your website
  3. In IIS go to advanced settings of application pool of your website
  4. Set "Enable 32-Bit Applications" property to "True"
  5. Restart the pool and your website
  6. Make a request to the site

Actual result:

in response headers value of "Content-Size" header is enormous. Thus client actually loads contents but waits for the rest. If you try to load your site in a common browser such as Chrome loading will hang up.