diff --git a/ethcore/src/block.rs b/ethcore/src/block.rs
index 88894618c..87f4749a1 100644
--- a/ethcore/src/block.rs
+++ b/ethcore/src/block.rs
@@ -205,7 +205,6 @@ pub struct ClosedBlock {
 	block: ExecutedBlock,
 	uncle_bytes: Bytes,
 	last_hashes: Arc<LastHashes>,
-	unclosed_state: State,
 }
 
 /// Just like `ClosedBlock` except that we can't reopen it and it's faster.
@@ -343,11 +342,12 @@ impl<'x> OpenBlock<'x> {
 		}
 	}
 
-	/// Turn this into a `ClosedBlock`. A `BlockChain` must be provided in order to figure out the uncles.
+	/// Turn this into a `ClosedBlock`.
 	pub fn close(self) -> ClosedBlock {
 		let mut s = self;
 
-		let unclosed_state = s.block.state.clone();
+		// take a snapshot so the engine's changes can be rolled back.
+		s.block.state.snapshot();
 
 		s.engine.on_close_block(&mut s.block);
 		s.block.base.header.set_transactions_root(ordered_trie_root(s.block.base.transactions.iter().map(|e| e.rlp_bytes().to_vec()).collect()));
@@ -362,14 +362,16 @@ impl<'x> OpenBlock<'x> {
 			block: s.block,
 			uncle_bytes: uncle_bytes,
 			last_hashes: s.last_hashes,
-			unclosed_state: unclosed_state,
 		}
 	}
 
-	/// Turn this into a `LockedBlock`. A BlockChain must be provided in order to figure out the uncles.
+	/// Turn this into a `LockedBlock`.
 	pub fn close_and_lock(self) -> LockedBlock {
 		let mut s = self;
 
+		// take a snapshot so the engine's changes can be rolled back.
+		s.block.state.snapshot();
+
 		s.engine.on_close_block(&mut s.block);
 		if s.block.base.header.transactions_root().is_zero() || s.block.base.header.transactions_root() == &SHA3_NULL_RLP {
 			s.block.base.header.set_transactions_root(ordered_trie_root(s.block.base.transactions.iter().map(|e| e.rlp_bytes().to_vec()).collect()));
@@ -381,14 +383,16 @@ impl<'x> OpenBlock<'x> {
 		if s.block.base.header.receipts_root().is_zero() || s.block.base.header.receipts_root() == &SHA3_NULL_RLP {
 			s.block.base.header.set_receipts_root(ordered_trie_root(s.block.receipts.iter().map(|r| r.rlp_bytes().to_vec()).collect()));
 		}
+
 		s.block.base.header.set_state_root(s.block.state.root().clone());
 		s.block.base.header.set_log_bloom(s.block.receipts.iter().fold(LogBloom::zero(), |mut b, r| {b = &b | &r.log_bloom; b})); //TODO: use |= operator
 		s.block.base.header.set_gas_used(s.block.receipts.last().map_or(U256::zero(), |r| r.gas_used));
 
-		LockedBlock {
+		ClosedBlock {
 			block: s.block,
 			uncle_bytes: uncle_bytes,
-		}
+			last_hashes: s.last_hashes,
+		}.lock()
 	}
 }
 
@@ -409,7 +413,17 @@ impl ClosedBlock {
 	pub fn hash(&self) -> H256 { self.header().rlp_sha3(Seal::Without) }
 
 	/// Turn this into a `LockedBlock`, unable to be reopened again.
-	pub fn lock(self) -> LockedBlock {
+	pub fn lock(mut self) -> LockedBlock {
+		// finalize the changes made by the engine.
+		self.block.state.clear_snapshot();
+		if let Err(e) = self.block.state.commit() {
+			warn!("Error committing closed block's state: {:?}", e);
+		}
+
+		// set the state root here, after commit recalculates with the block
+		// rewards.
+		self.block.base.header.set_state_root(self.block.state.root().clone());
+
 		LockedBlock {
 			block: self.block,
 			uncle_bytes: self.uncle_bytes,
@@ -417,12 +431,12 @@ impl ClosedBlock {
 	}
 
 	/// Given an engine reference, reopen the `ClosedBlock` into an `OpenBlock`.
-	pub fn reopen(self, engine: &Engine) -> OpenBlock {
+	pub fn reopen(mut self, engine: &Engine) -> OpenBlock {
 		// revert rewards (i.e. set state back at last transaction's state).
-		let mut block = self.block;
-		block.state = self.unclosed_state;
+		self.block.state.revert_snapshot();
+
 		OpenBlock {
-			block: block,
+			block: self.block,
 			engine: engine,
 			last_hashes: self.last_hashes,
 		}
diff --git a/ethcore/src/ethereum/ethash.rs b/ethcore/src/ethereum/ethash.rs
index 216ebed17..734acb758 100644
--- a/ethcore/src/ethereum/ethash.rs
+++ b/ethcore/src/ethereum/ethash.rs
@@ -167,9 +167,7 @@ impl Engine for Ethash {
 		for u in fields.uncles.iter() {
 			fields.state.add_balance(u.author(), &(reward * U256::from(8 + u.number() - current_number) / U256::from(8)));
 		}
-		if let Err(e) = fields.state.commit() {
-			warn!("Encountered error on state commit: {}", e);
-		}
+
 	}
 
 	fn verify_block_basic(&self, header: &Header, _block: Option<&[u8]>) -> result::Result<(), Error> {
diff --git a/ethcore/src/state/mod.rs b/ethcore/src/state/mod.rs
index 8c7e49ba3..78eb01c7c 100644
--- a/ethcore/src/state/mod.rs
+++ b/ethcore/src/state/mod.rs
@@ -420,10 +420,27 @@ impl fmt::Debug for State {
 
 impl Clone for State {
 	fn clone(&self) -> State {
+		let cache = {
+			let mut cache = HashMap::new();
+			for (key, val) in self.cache.borrow().iter() {
+				let key = key.clone();
+				match *val {
+					Some(ref acc) if acc.is_dirty() => {
+						cache.insert(key, Some(acc.clone()));
+					},
+					None => {
+						cache.insert(key, None);
+					},
+					_ => {},
+				}
+			}
+			cache
+		};
+
 		State {
 			db: self.db.boxed_clone(),
 			root: self.root.clone(),
-			cache: RefCell::new(self.cache.borrow().clone()),
+			cache: RefCell::new(cache),
 			snapshots: RefCell::new(self.snapshots.borrow().clone()),
 			account_start_nonce: self.account_start_nonce.clone(),
 			factories: self.factories.clone(),