I managed to work around this problem:
This is the content of my POST request I was having:
To solve this problem I used a jquery plugin to handle the form (
http://jquery.malsup.com/form/) this is the POST request content after the change:
The only difference I can find is the User-Agent property... I'm not really sure what helped solving this, my clue was that somehow IE was not handling correctly the request, so I tried to change the behavior via javascript...