diff --git a/packages/runner/src/runner-utils.ts b/packages/runner/src/runner-utils.ts
index c15bc246c5..ce673aa8cc 100644
--- a/packages/runner/src/runner-utils.ts
+++ b/packages/runner/src/runner-utils.ts
@@ -726,6 +726,7 @@ function mergeSchemaDefaultsInternal(
 
     const existing = valuePresent ? value as Record<string, unknown> : {};
     const result: Record<string, unknown> = { ...existing };
+    let unchanged = valuePresent;
     // Object-shaped unions (including Common Fabric's non-standard
     // `type: ["object", "undefined"]`) still need presence-aware merging. A
     // generic merge cannot distinguish an absent property from an own property
@@ -773,6 +774,7 @@ function mergeSchemaDefaultsInternal(
           }) === undefined
         )
       ) {
+        unchanged &&= hasExistingValue && Object.is(merged, existing[key]);
         Object.defineProperty(result, key, {
           value: merged,
           enumerable: true,
@@ -781,7 +783,7 @@ function mergeSchemaDefaultsInternal(
         });
       }
     }
-    return valuePresent && schemaDefaultValueEqual(result, value)
+    return unchanged || (valuePresent && schemaDefaultValueEqual(result, value))
       ? value
       : result;
   } finally {