diff --git a/yarn-project/aztec-node/src/aztec-node/server.ts b/yarn-project/aztec-node/src/aztec-node/server.ts
index 29ecf74d8e1..5cbfcfab8d1 100644
--- a/yarn-project/aztec-node/src/aztec-node/server.ts
+++ b/yarn-project/aztec-node/src/aztec-node/server.ts
@@ -88,7 +88,7 @@ export class AztecNodeService implements AztecNode {
     const p2pClient = await createP2PClient(config, new InMemoryTxPool(), archiver);
 
     // now create the merkle trees and the world state syncher
-    const merkleTreeDB = await MerkleTrees.new(levelup(createMemDown()), await CircuitsWasm.get());
+    const merkleTreeDB = await AztecNodeService.createMerkleTreeDB();
     const worldStateConfig: WorldStateConfig = getWorldStateConfig();
     const worldStateSynchroniser = new ServerWorldStateSynchroniser(merkleTreeDB, archiver, worldStateConfig);
 
@@ -119,6 +119,10 @@ export class AztecNodeService implements AztecNode {
     );
   }
 
+  static async createMerkleTreeDB() {
+    return MerkleTrees.new(levelup(createMemDown()), await CircuitsWasm.get());
+  }
+
   /**
    * Method to determine if the node is ready to accept transactions.
    * @returns - Flag indicating the readiness for tx submission.
@@ -382,16 +386,17 @@ export class AztecNodeService implements AztecNode {
    **/
   public async simulatePublicPart(tx: Tx) {
     this.log.info(`Simulating tx ${await tx.getTxHash()}`);
+    // Instantiate merkle tree db so uncommited updates by this simulation are local to it.
+    const merkleTreeDb = await AztecNodeService.createMerkleTreeDB();
 
     const publicProcessorFactory = new PublicProcessorFactory(
-      this.worldStateSynchroniser.getLatest(),
+      merkleTreeDb.asLatest(),
       this.contractDataSource,
       this.l1ToL2MessageSource,
     );
     const blockNumber = (await this.blockSource.getBlockNumber()) + 1;
     const newGlobalVariables = await this.globalVariableBuilder.buildGlobalVariables(new Fr(blockNumber));
     const prevGlobalVariables = (await this.blockSource.getL2Block(-1))?.globalVariables ?? GlobalVariables.empty();
-
     const processor = await publicProcessorFactory.create(prevGlobalVariables, newGlobalVariables);
     const [, failedTxs] = await processor.process([tx]);
     if (failedTxs.length) {
diff --git a/yarn-project/sequencer-client/src/sequencer/sequencer.ts b/yarn-project/sequencer-client/src/sequencer/sequencer.ts
index 35748885af4..eb7dc60bf76 100644
--- a/yarn-project/sequencer-client/src/sequencer/sequencer.ts
+++ b/yarn-project/sequencer-client/src/sequencer/sequencer.ts
@@ -147,7 +147,8 @@ export class Sequencer {
       // Process txs and drop the ones that fail processing
       // We create a fresh processor each time to reset any cached state (eg storage writes)
       const processor = await this.publicProcessorFactory.create(prevGlobalVariables, newGlobalVariables);
-      const [processedTxs, failedTxs] = await processor.process(validTxs);
+      // The processor modifies the tx objects in place, so we need to clone them.
+      const [processedTxs, failedTxs] = await processor.process(validTxs.map(tx => Tx.fromJSON(tx.toJSON())));
       if (failedTxs.length > 0) {
         const failedTxData = failedTxs.map(fail => fail.tx);
         this.log(`Dropping failed txs ${(await Tx.getHashes(failedTxData)).join(', ')}`);