KB Article: http://support.microsoft.com/kb/2591803

INTRODUCTION

Consider the following scenario:

• A web proxy client establishes a secure socket layer (SSL) connection to an external web server by using a server that is running Microsoft Forefront Threat Management Gateway 2010.
• HTTPS inspection is not involved. Therefore, an end-to-end SSL tunnel between the client and the web server is established.
• Inside this established connection, the client uploads data to the web server.
• The connection and TCP flow to the web server are slow.

In this scenario, the upload does not finish correctly under certain circumstances.