master commit 969519b3b53e1ba12a261764fc4d5785524a245f has not been merged into v4-2-stable. This makes bkrp_do_retrieve_server_wrap_key fail:
[2015/07/24 13:21:28.496186, 1, pid=3509] ../source4/rpc_server/backupkey/dcesrv_backupkey.c:1423(bkrp_do_retrieve_server_wrap_key)
Unable to fetch value for secret BCKUPKEY_01234567-0123-0123-0123-0123456789ab, are we an undetected RODC?
Maybe this is message correlates with user reports of failing to unlock their Windows desktop after the server was updated to 4.2.0 or later.
Volkers commit https://git.samba.org/?p=samba.git;a=commit;h=969519b3b53e1ba12a261764fc4d5785524a245f in master should be merged to v4-2-stable in order to fix this. There are 4 additional commits around that should be considered as well.
+++ This bug was initially created as a clone of Bug #11097 +++
Thanks for this report. FIXED isn't a really good tag, because it is only fixed in 4.3 and above, but 4.2 is out of support except for security fixes.
However this is a very good place-holder to remind those issuing 4.2 packages to pick up this change, particularly if upgrading from 4.1.