SpringLDAPConnector returns ImmutableList which can't be sorted by ViewGroupMembers class

I already raised a support issue but they said that this is more of a developer question. So i try to explain it here since i really think this is a bug:

We are trying to update to Crowd Version 2.6.0 from Crowd Version 2.5.0. We are running our own implementation of a LDAP directory based on the OpenDS.java class.
So far our implementation ran fine. Except we are getting a exception when viewing Direct Members of a Group:

2013-02-25 11:34:31,948 http-8095-5 ERROR [console.action.group.ViewGroupMembers] 
java.lang.UnsupportedOperationException
	at com.google.common.collect.UnmodifiableListIterator.set(UnmodifiableListIterator.java:51)
	at java.util.Collections.sort(Collections.java:161)
	at com.atlassian.crowd.console.action.group.ViewGroupMembers.execute(ViewGroupMembers.java:60)

None of the code we added was involved, so i tried to nail the problem down.
I got myself the source of the 2.6.0 Crowd. After some searching i found the following lines inside the ViewGroupMembers class:

List<User> principalsList = directoryManager.searchDirectGroupRelationships(directoryID, QueryBuilder.queryFor(User.class, EntityDescriptor.user()).childrenOf(EntityDescriptor.group(GroupType.GROUP)).withName(groupName).returningAtMost(EntityQuery.ALL_RESULTS));
                Collections.sort(principalsList, EntityComparator.of(User.class));
                principals = principalsList; // sort the list

The sorting is where the exception happens.
The used line in your basic SpringLDAPConnector.java implementation shows that the used method returns a ImmutableList:

Line 1415:
        return ImmutableList.copyOf(results);

This is different from the Version 2.5.0 of the SpringLDAPConnector.java, there on line 1396 only the result without converting it to a ImmutableList is returned.

I dont know if this is a problem with other people too or am i missing something here ?