I think if you're using grouperLoaderLdapGroupNameExpression in such a way that multiple LDAP attribute values are translating into the same group name using EL, then all memberships may not get added.

This may just be a couple line fix:

In GrouperLoaderResultset:

From:

918 //init the subject list
919 result.put(groupName, new ArrayList<String>());

To:

918 //init the subject list
919 if (!result.containsKey(groupName))

{ 920 result.put(groupName, new ArrayList<String>()); 921 }

???