diff --git a/miner/miner.go b/miner/miner.go
index <HASH>..<HASH> 100644
--- a/miner/miner.go
+++ b/miner/miner.go
@@ -48,14 +48,16 @@ func (self *Miner) Start(coinbase common.Address) {
 }
 
 func (self *Miner) Register(agent Agent) {
+	if self.mining {
+		agent.Start()
+	}
+
 	self.worker.register(agent)
 }
 
 func (self *Miner) Stop() {
 	self.mining = false
 	self.worker.stop()
-
-	//self.pow.(*ethash.Ethash).Stop()
 }
 
 func (self *Miner) HashRate() int64 {
diff --git a/miner/worker.go b/miner/worker.go
index <HASH>..<HASH> 100644
--- a/miner/worker.go
+++ b/miner/worker.go
@@ -225,7 +225,11 @@ func (self *worker) push() {
 		for _, agent := range self.agents {
 			atomic.AddInt64(&self.atWork, 1)
 
-			agent.Work() <- self.current.block.Copy()
+			if agent.Work() != nil {
+				agent.Work() <- self.current.block.Copy()
+			} else {
+				common.Report(fmt.Sprintf("%v %T\n", agent, agent))
+			}
 		}
 	}
 }
miner: start a newly registered agent if the miner is running. Closes #<I>