diff --git a/src/interfaces/mining.h b/src/interfaces/mining.h
index a30c4afb526..6e0376915d8 100644
--- a/src/interfaces/mining.h
+++ b/src/interfaces/mining.h
@@ -54,9 +54,22 @@ public:
     virtual std::vector<uint256> getCoinbaseMerklePath() = 0;
 
     /**
-     * Construct and broadcast the block.
+     * Construct and broadcast the block. Modifies the template in place,
+     * updating the fields listed below as well as the merkle root.
      *
-     * @returns if the block was processed, independent of block validity
+     * @param[in] version version block header field
+     * @param[in] timestamp time block header field (unix timestamp)
+     * @param[in] nonce nonce block header field
+     * @param[in] coinbase complete coinbase transaction (including witness)
+     *
+     * @note unlike the submitblock RPC, this method does NOT add the
+     *       coinbase witness automatically.
+     *
+     * @returns if the block was processed, does not necessarily indicate validity.
+     *
+     * @note Returns true if the block is already known, which can happen if
+     *       the solved block is constructed and broadcast by multiple nodes
+     *       (e.g. both the miner who constructed the template and the pool).
      */
     virtual bool submitSolution(uint32_t version, uint32_t timestamp, uint32_t nonce, CTransactionRef coinbase) = 0;
 
diff --git a/src/node/miner.cpp b/src/node/miner.cpp
index 39f0879ce2c..14e5ce0a7be 100644
--- a/src/node/miner.cpp
+++ b/src/node/miner.cpp
@@ -452,6 +452,11 @@ void AddMerkleRootAndCoinbase(CBlock& block, CTransactionRef coinbase, uint32_t
     block.nTime = timestamp;
     block.nNonce = nonce;
     block.hashMerkleRoot = BlockMerkleRoot(block);
+
+    // Reset cached checks
+    block.m_checked_witness_commitment = false;
+    block.m_checked_merkle_root = false;
+    block.fChecked = false;
 }
 
 void InterruptWait(KernelNotifications& kernel_notifications, bool& interrupt_wait)
diff --git a/src/validation.h b/src/validation.h
index 291c1021dc9..cd448f3ca9e 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -1276,7 +1276,11 @@ public:
     //! ResizeCoinsCaches() as needed.
     void MaybeRebalanceCaches() EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
 
-    /** Update uncommitted block structures (currently: only the witness reserved value). This is safe for submitted blocks. */
+    /**
+     * Update uncommitted block structures (currently: only the witness reserved
+     * value). This is safe for submitted blocks as long as they honor
+     * default_witness_commitment from the template.
+     */
     void UpdateUncommittedBlockStructures(CBlock& block, const CBlockIndex* pindexPrev) const;
 
     /** Produce the necessary coinbase commitment for a block (modifies the hash, don't call for mined blocks). */
diff --git a/test/functional/interface_ipc.py b/test/functional/interface_ipc.py
index a4b57ece2d1..23036649529 100755
--- a/test/functional/interface_ipc.py
+++ b/test/functional/interface_ipc.py
@@ -8,7 +8,11 @@ from io import BytesIO
 from pathlib import Path
 import shutil
 from test_framework.messages import (CBlock, CTransaction, ser_uint256, COIN)
-from test_framework.test_framework import (BitcoinTestFramework, assert_equal)
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import (
+    assert_equal,
+    assert_not_equal
+)
 from test_framework.wallet import MiniWallet
 
 # Test may be skipped and not have capnp installed
@@ -49,10 +53,10 @@ class IPCInterfaceTest(BitcoinTestFramework):
         }
 
     def set_test_params(self):
-        self.num_nodes = 1
+        self.num_nodes = 2
 
     def setup_nodes(self):
-        self.extra_init = [{"ipcbind": True}]
+        self.extra_init = [{"ipcbind": True}, {}]
         super().setup_nodes()
         # Use this function to also load the capnp modules (we cannot use set_test_params for this,
         # as it is being called before knowing whether capnp is available).
@@ -228,11 +232,35 @@ class IPCInterfaceTest(BitcoinTestFramework):
             self.log.debug("Submit a valid block")
             block.nVersion = original_version
             block.solve()
+
+            self.log.debug("First call checkBlock()")
             res = await mining.result.checkBlock(block.serialize(), check_opts)
             assert_equal(res.result, True)
+
+            # The remote template block will be mutated, capture the original:
+            remote_block_before = await self.parse_and_deserialize_block(template, ctx)
+
+            self.log.debug("Submitted coinbase must include witness")
+            assert_not_equal(coinbase.serialize_without_witness().hex(), coinbase.serialize().hex())
+            res = await template.result.submitSolution(ctx, block.nVersion, block.nTime, block.nNonce, coinbase.serialize_without_witness())
+            assert_equal(res.result, False)
+
+            self.log.debug("Even a rejected submitBlock() mutates the template's block")
+            # Can be used by clients to download and inspect the (rejected)
+            # reconstructed block.
+            remote_block_after = await self.parse_and_deserialize_block(template, ctx)
+            assert_not_equal(remote_block_before.serialize().hex(), remote_block_after.serialize().hex())
+
+            self.log.debug("Submit again, with the witness")
             res = await template.result.submitSolution(ctx, block.nVersion, block.nTime, block.nNonce, coinbase.serialize())
             assert_equal(res.result, True)
-            assert_equal(self.nodes[0].getchaintips()[0]["height"], current_block_height + 1)
+
+            self.log.debug("Block should propagate")
+            assert_equal(self.nodes[1].getchaintips()[0]["height"], current_block_height + 1)
+            # Stalls if a regression causes submitBlock() to accept an invalid block:
+            self.sync_all()
+            assert_equal(self.nodes[0].getchaintips()[0], self.nodes[1].getchaintips()[0])
+
             miniwallet.rescan_utxos()
             assert_equal(miniwallet.get_balance(), balance + 1)
             self.log.debug("Check block should fail now, since it is a duplicate")