diff --git a/v4/ctx_test2.cpp b/v4/ctx_test2.cpp
index 5ddfbdf..9317244 100644
--- a/v4/ctx_test2.cpp
+++ b/v4/ctx_test2.cpp
@@ -88,3 +88,31 @@ std::string test_ctx_Controller_registerFieldCallback_match() {
   }
   return "ERR: ctx_Controller_registerFieldCallback_match";
 }
+
+std::string test_ctx_Controller_registerFieldCallback_mismatch() {
+  auto c = memory_createContext();
+  ctx_Controller<memory_Context> ctrl(c);
+
+  c.input = "123";
+  c.outputHelp = "you";
+  // A field other than 'input' is marked recent.
+  c.recentField = "outputHelp";
+  std::string callbackInput = "";
+
+  auto setCallbackInput = [&callbackInput](memory_Context c) {
+    if (
+      c.recentField == "input"
+    ) {
+      callbackInput = c.input;
+    }
+  };
+
+  ctrl.registerFieldCallback("input", setCallbackInput);
+  ctrl.reportContext();
+  if (
+    callbackInput == ""
+  ) {
+    return "OK: ctx_Controller_registerFieldCallback_mismatch";
+  }
+  return "ERR: ctx_Controller_registerFieldCallback_mismatch";
+}
diff --git a/v4/ctx_test2.h b/v4/ctx_test2.h
index b01d057..8f2ea17 100644
--- a/v4/ctx_test2.h
+++ b/v4/ctx_test2.h
@@ -6,5 +6,6 @@
 std::string test_ctx_Controller_executeFunctions_set();
 std::string test_ctx_Controller_processQueue();
 std::string test_ctx_Controller_registerFieldCallback_match();
+std::string test_ctx_Controller_registerFieldCallback_mismatch();
 
 #endif // ctx_test_HEADER
diff --git a/v4/ctx_test2.py b/v4/ctx_test2.py
index 3d1fd58..cde26fd 100644
--- a/v4/ctx_test2.py
+++ b/v4/ctx_test2.py
@@ -113,7 +113,7 @@ def ctx_test_Controller_registerFieldCallback_mismatch(
   ):
     return "OK: ctx_Controller_registerFieldCallback_mismatch"
   #}
-  return f"ERR: ctx_Controller_registerFieldCallback_mismatch"
+  return "ERR: ctx_Controller_registerFieldCallback_mismatch"
 #}
 
 def ctx_test_memoryContext_field(
diff --git a/v4/main.cpp b/v4/main.cpp
index 84cb9c0..5a37b7d 100644
--- a/v4/main.cpp
+++ b/v4/main.cpp
@@ -13,6 +13,8 @@ int main() {
     << std::endl
     << test_ctx_Controller_registerFieldCallback_match()
     << std::endl
+    << test_ctx_Controller_registerFieldCallback_mismatch()
+    << std::endl
     << llm_test_isDigit_digit()
     << std::endl
     << llm_test_isDigit_notDigit()