LDAP user counts as uniqueMember for group but is not present in uniqueMember list

Question

A user left the organization, so I removed him from all of his groups. Afterward, he still seems to be in one group but not in the group's members. See below:

[bauron@ldapmaster ~]$ ldapsearch -x -b"dc=domain,dc=com" "(uniqueMember=uid=TARGETUSER,ou=users,dc=domain,dc=com)" dn uniqueMember
# extended LDIF
#
# LDAPv3
# base <dc=domain,dc=com> with scope subtree
# filter: (uniqueMember=uid=TARGETUSER,ou=users,dc=domain,dc=com)
# requesting: dn uniqueMember
#

# jca, roles, groups, domain.com
dn: cn=jca,ou=roles,ou=groups,dc=domain,dc=com
uniqueMember: uid=user1,ou=users,dc=domain,dc=com
uniqueMember: uid=user2,ou=users,dc=domain,dc=com
uniqueMember: uid=user3,ou=users,dc=domain,dc=com
... # rest of list omitted

# search result
search: 2
result: 0 Success

# numResponses: 2
# numEntries: 1
[bauron@ldapmaster ~]$ ldapsearch -x -b"dc=domain,dc=com" "(uniqueMember=uid=TARGETUSER,ou=users,dc=domain,dc=com)" dn uniqueMember | grep TARGETUSER
# filter: (uniqueMember=uid=TARGETUSER,ou=users,dc=domain,dc=com)
[bauron@ldapmaster ~]$

As you can see, grep'ing the list for TARGETUSER fails even though I'm explicitly asking for groups which have TARGETUSER as a uniqueMember. I have no idea how this is possible or what I can do to fix it. Thanks in advance!