samba - May 2014 - Intermittent Delays in Listing Large Directory

Hello,

I am running a Samba 3.6.3 server on Ubuntu 12.04. One directory on a share
called MyShare contains a lot of direct subdirectories - around 1800.
Intermittently, users will experience 10-60 second delays when attempting to
list the contents of this directory (Explorer on Windows 7 clients). Most of the
time listing the contents of this large directory is fast, but occasionally it
is very slow. During one of these slow events, I captured the samba log for said
client computer:
http://pastebin.com/tLXJmE5D

Also, here is my smb.conf:
http://pastebin.com/QmM52Lx1

What can I try to debug this issue further? What could be causing this
intermittent delay in listing the directory contents?

Thanks,

Andrew