This issue occurs because Web Application Proxy (WAP) cannot handle other request status other than a success status. When the http.sys request object exceeds the 16-kilobyte (KB) limit of the WAP buffer, WAP cannot handle the request, and therefore it leaves the request in the http.sys queue.
Note The size of the http.sys request object is at least three times the size of the URI. Therefore, if the size of a URI is more than 5,100 bytes, the size of the request object will exceed the 16-KB limit.
To resolve this issue, install the December 2014 update rollup for Windows RT 8.1, Windows 8.1, and Windows Server 2012 R2.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Learn about the terminology that Microsoft uses to describe software updates.