[INFO] [02/26/2014 17:56:28.472] [application-akka.actor.default-dispatcher-17] [akka://application/deadLetters] Message [models.service.ServiceBuckets] from Actor[akka://application/user/$v#-1897069859] to Actor[akka://application/deadLetters] was not delivered.  dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.
Thanks for posting your own answer - seems like you are the local Akka expert!
I know almost nothing about Akka, but I just looked in Akka Concurrency by Derek Wyatt, where he mentions (p.102) that the dead letter office is used as a default sender if you don't provide one. Also, it says in there that "sender" is actually a method, not a value, which might be why you need to create the val newSender in order to access the sender instance from an incoming message, then use this newSender value for your next message.
The dead letter log messages may or may not be a sign of a problem according to this documentation.
Anybody else out there know enough Akka to help Khuma properly here?