diff --git a/core/state/statedb.go b/core/state/statedb.go
index e51fcd2cfe..abf0a02a87 100644
--- a/core/state/statedb.go
+++ b/core/state/statedb.go
@@ -577,7 +577,8 @@ func (s *StateDB) updateStateObject(obj *stateObject) {
 	}
 }
 
-// updateStateObject writes the given object to the trie.
+// updateStateObject writes the given object to the trie.  The actual value is
+// only resolved from the provided function when it is needed during trie hashing.
 func (s *StateDB) updateStateObjectAsync(addr common.Address, resolver func() *types.StateAccount) {
 	if err := s.trie.UpdateAccountAsync(addr, resolver); err != nil {
 		s.setError(fmt.Errorf("updateStateObject (%x) error: %v", addr, err))
diff --git a/tests/testdata b/tests/testdata
index 81862e4848..c67e485ff8 160000
--- a/tests/testdata
+++ b/tests/testdata
@@ -1 +1 @@
-Subproject commit 81862e4848585a438d64f911a19b3825f0f4cd95
+Subproject commit c67e485ff8b5be9abc8ad15345ec21aa22e290d9
diff --git a/trie/secure_trie.go b/trie/secure_trie.go
index b48d28199b..4c8a181acf 100644
--- a/trie/secure_trie.go
+++ b/trie/secure_trie.go
@@ -226,6 +226,9 @@ func (t *StateTrie) UpdateAccount(address common.Address, acc *types.StateAccoun
 	return nil
 }
 
+// UpdateAccountAsync will abstract the write of an account to the secure trie.
+// The actual value of the account is not resolved from the passed function until
+// it is needed when hashing the trie.
 func (t *StateTrie) UpdateAccountAsync(address common.Address, accountResolve func() *types.StateAccount) error {
 	hk := crypto.Keccak256(address.Bytes())
 	resolve := func() []byte {
diff --git a/trie/trie.go b/trie/trie.go
index ec84a038da..eb64d1f7c9 100644
--- a/trie/trie.go
+++ b/trie/trie.go
@@ -382,6 +382,8 @@ func (t *Trie) Update(key, value []byte) error {
 	return t.update(key, value)
 }
 
+// UpdateAsync associates a key with value in the trie.  The actual value is
+// not resolved until needed (by calling Get, or Hash).
 func (t *Trie) UpdateAsync(key []byte, valueResolver func() []byte) error {
 	t.unhashed++
 	t.uncommitted++