fix #499

h2/src/main/org/h2/mvstore/db/TransactionStore.java

@@ -350,8 +350,12 @@ public class TransactionStore {
                     if (value == null) {
                         // nothing to do
                     } else if (value.value == null) {
-                        // remove the value
-                        map.remove(key);
+                        int tx = getTransactionId(value.operationId);
+                        if (tx == t.transactionId) {
+                            // remove the value
+                            // only if it's transaction id is same as current transaction id
+                            map.remove(key);
+                        }
                     } else {
                         VersionedValue v2 = new VersionedValue();
                         v2.value = value.value;