URL Rewrite module interference

I've been using Glimpse on an asp.net mvc 3 project (.net 4.0) together with IIS Url Rewrite module. I've noticed that when Glimpse `defaultRuntimePolicy="On"` URL Rewrite module has troubles properly handling POST requests. 
I've created separate project and was able to reproduce the issue:
* asp.net mvc 3 
* .net 4
* Glimpse.1.4.2
* Glimpse.AspNet.1.3.1
* Glimpse.Mvc3.1.3.2 

After quick investigation I've found that a root cause of the problem is in `RequestMetadata.RequestIsAjax` method which is called by `AjaxPolicy`. From my understanding the `request["X-Requested-With"]` call causes the http POST body to be read thus making the underlying request network stream not accessible to URL Rewrite or any other native module.  

This issue may be related to https://github.com/Glimpse/Glimpse/issues/469