I'm seeing this issue too on 5.2.0.26.1, running LDAP auth through a F5 Load Balancer to a pair of Sun directory servers.
Did you make any progress with your TAC case?
Without using the root patch, this command is useful for finding out what is going on (it's just netstat):
# show tech-support | i ldap | i tcp
ldap 389/tcp
ldaps 636/tcp # LDAP over SSL
tcp 0 0 exc2-acscor-1401:53892 acs.ldapunix.co:ldap ESTABLISHED
tcp 0 0 exc2-acscor-1401:53893 acs.ldapunix.co:ldap ESTABLISHED
tcp 0 0 exc2-acscor-1401:53890 acs.ldapunix.co:ldap ESTABLISHED
tcp 0 0 exc2-acscor-1401:53891 acs.ldapunix.co:ldap ESTABLISHED
tcp 0 0 exc2-acscor-1401:53889 acs.ldapunix..co:ldap ESTABLISHED
Also try adjusting "Max. Admin Connections" for LDAP.
From the admin guide:
LDAP Connection Management
ACS 5.1 supports multiple concurrent LDAP connections. Connections are opened on demand at the time of the first LDAP authentication. The maximum number of connections is configured for each LDAP server. Opening connections in advance shortens the authentication time. You can set the maximum number of connections to use for concurrent binding connections. The number of opened connections can be different for each LDAP server (primary or secondary) and is determined according to the maximum number of administration connections configured for each server.
ACS retains a list of open LDAP connections (including the bind information) for each LDAP server that is configured in ACS. During the authentication process, the connection manager attempts to find an open connection from the pool. If an open connection does not exist, a new one is opened.
If the LDAP server closed the connection, the connection manager reports an error during the first call to search the directory, and tries to renew the connection.
After the authentication process is complete, the connection manager releases the connection to the connection manager.
I'd be interested to hear if you have fixed your issue, or if anyone else is facing similar problems load balancing LDAP servers for the ACS.
Cheers
R.