samba - Jul 2013 - Samba server does not drop connection after client disconnect

Samba Version: 3.6.10
Windows Client:  Windows 7

A Windows client laptop has a wired internet connection.
The Windows client has a file open on the Samba CIFS share.
The client is then disconnected from the network (network cable removed).
The client connection drops almost immediately, but the Samba server side
connection remains for over 15 minutes.
This prevents the user from opening the file using the wireless connection from
the laptop to access the locked file.
I tried setting the keepalive parameter to 20 seconds but this had no effect.

Any suggestions?

Thanks