Problem with iRule ProxyPass v10 and "/" URI

We have the same result with some different Browser (IE 6, IE 8, Firefox ...) so I don't think it's a problem with browsers but i'm not sure.

I have not capture between F5 and server at this time because it's ssl encrypted and we didn't succeed to decrypt them (we have the same certificate between client-->F5 and F5--> server but it doesn't decrypt and I don't know why). We have some capture between client to f5 with the response send by the F5 and we have a difference between the path "/" and an other path as "/ent/"

Please see below with path "/" :

HTTP/1.1 200 OK Server: Sun-ONE-Web-Server/6.1 Date: Thu, 06 Feb 2014 14:34:39 GMT Content-type: text/html;charset=UTF-8 Content-language: fr Cache-control: no-cache Pragma: no-cache **Set-Cookie: _sn=clk9cVxtMmc-tbOq1WTwKdrCnRLVUqm8WNMEL4JtUW0_; Version=1; Path=/ent_gcdn_fra; HTTPOnly** Transfer-Encoding: chunked

and with path "/ent" : 
HTTP/1.1 200 OK
Server: Sun-ONE-Web-Server/6.1
Date: Thu, 06 Feb 2014 14:40:21 GMT
Content-type: text/html;charset=UTF-8
Pragma: no-cache
Content-language: fr
Cache-control: no-cache, must-revalidate, max-age=0
Pragma: no-cache
**Set-Cookie: _sn=8bU9RNnaRJjJttXPViTrzkZCH135Tf-Pl0lQ5mfutHU_; Version=1; Path=/ent; HTTPOnly**
Transfer-Encoding: chunked

As you can see, for the path "/", the path of the set-cookie is not just "/" that is not good for me. For the path "/ent", the path of the cookie is "/ent, that it's good for me. 

Many thanks