This bug was submitted through http://support.atlassian.com and was confirmed:

When I go to the Principals page to search for a user (i.e. "stephen tang"), I noticed the Crowd log shows something like this:

14:33:21,366 INFO crowd.integration.directory.connector.SpringLDAPConnector: Performing search: baseDN = OU=Studios,dc=company,dc=com - filter = (&(sAMAccountName=john doe)(objectClass=person))

When I try to put something more complicated into the User Object Filter field, like:

(&(&(objectClass=user)(objectClass=organizationalPerson))(!objectClass=computer))), Crowd complains that the parentheses are unbalanced. The log shows:

15:39:08,346 INFO crowd.integration.directory.connector.SpringLDAPConnector: Performing principal search: baseDN = ou=Users, ou=Studios,OU=Studios,dc=company,dc=com - filter = (&(sAMAccountName=john doe)(&(&(objectClass=user)(objectClass=organizationalPerson))(!objectClass=computer)))

Which results in the following error:

Invalid search filter; nested exception is javax.naming.directory.InvalidSearchFilterException: Unbalanced parenthesis; ...