LdapAuthentication creates MediaWiki groups to sync with LDAP groups, using the $wgLDAPUseLDAPGroups setting, When the LDAP group name contains whitespace, LdapAuthentication will happily create a MediaWiki group with the identical name, even though whitespace is invalid in MediaWiki group names.
As a result, Special:UserRights cannot handle these groups. If you try to add a group, the add silently fails. If you are a member of one of these groups, and you perform ANY submission on Special:UserRights, you get unexpectedly removed from the group.
LdapAuthentication should modify the group names to get rid of any whitespace (for example, replacing spaces with underscores) when creating the MediaWiki groups.