smbpasswd has 10 debug levels specified by the -D switch. Level 10 is not recommended: the man page says "Levels above 3 are designed for use only by developers and generate HUGE amounts of log data, most of which is extremely cryptic." Really?
smbpasswd -D 10 -a testuser
gives us this:
smbldap_search_domain_info: Searching for:[(&(objectClass=sambaDomain)(sambaDomainName=RIVERSIDE))]
smbldap_search_ext: base => [dc=riverside,dc=forensit,dc=com], filter => [(&(objectClass=sambaDomain)(sambaDomainName=RIVERSIDE))], scope => 
The connection to the LDAP server was closed
smbldap_open_connection: connection opened
ldap_connect_system: Binding to ldap server ldap://riverside.forensit.com as "cn=Directory Manager"
ldap_connect_system: successful connection to the LDAP server
ldap_connect_system: LDAP server does not support paged results
The LDAP server is successfully connected
pdb backend ldapsam:ldap://riverside.forensit.com has a valid init
smbldap_search_ext: base => [dc=riverside,dc=forensit,dc=com], filter => [(&(uid=testuser)(objectclass=sambaSamAccount))], scope => 
ldapsam_getsampwnam: Unable to locate user [testuser] count=0
testuser can't be found. Of course it can't be found - we're trying to create it!