https://qt-project.atlassian.net/browse/QTBUG-142331
https://mail.kde.org/pipermail/distributions/2025-December/001648.html
https://bugs.kde.org/show_bug.cgi?id=512754
https://codereview.qt-project.org/c/qt/qtdeclarative/+/696524
--- a/src/qml/jsruntime/qv4lookup_p.h
+++ b/src/qml/jsruntime/qv4lookup_p.h
@@ -160,4 +160,8 @@
         } qobjectMethodLookup;
         struct {
+            // NB: None of this is actually cache-able. The metaobject may change at any time.
+            //     We invalidate this data every time the lookup is invoked and thereby force a
+            //     re-initialization next time.
+
             quintptr isConstant; // This is a bool, encoded as 0 or 1. Both values are ignored by gc
             quintptr metaObject; // a (const QMetaObject* & 1) or nullptr
--- a/src/qml/qml/qqml.cpp
+++ b/src/qml/qml/qqml.cpp
@@ -1378,14 +1378,14 @@
 static FallbackPropertyQmlData findFallbackPropertyQmlData(QV4::Lookup *lookup, QObject *object)
 {
+    // We've just initialized the lookup. So everything must be fine here.
+
     QQmlData *qmlData = QQmlData::get(object);
-    if (qmlData && qmlData->isQueuedForDeletion)
-        return {qmlData, nullptr, PropertyResult::Deleted};
 
+    Q_ASSERT(!qmlData || !qmlData->isQueuedForDeletion);
     Q_ASSERT(!QQmlData::wasDeleted(object));
 
     const QMetaObject *metaObject
             = reinterpret_cast<const QMetaObject *>(lookup->qobjectFallbackLookup.metaObject - 1);
-    if (!metaObject || metaObject != object->metaObject())
-        return {qmlData, nullptr, PropertyResult::NeedsInit};
+    Q_ASSERT(metaObject == object->metaObject());
 
     return {qmlData, metaObject, PropertyResult::OK};
@@ -2577,4 +2577,5 @@
     case QV4::Lookup::Call::ContextGetterScopeObjectPropertyFallback:
         result = loadFallbackProperty(lookup, qmlScopeObject, target, this);
+        lookup->call = QV4::Lookup::Call::ContextGetterGeneric;
         break;
     default:
@@ -2608,4 +2609,5 @@
     case QV4::Lookup::Call::ContextGetterScopeObjectPropertyFallback:
         result = writeBackFallbackProperty(lookup, qmlScopeObject, source);
+        lookup->call = QV4::Lookup::Call::ContextGetterGeneric;
         break;
     default:
@@ -2808,4 +2810,5 @@
                 ? loadFallbackAsVariant(lookup, object, target, this)
                 : loadFallbackProperty(lookup, object, target, this);
+        lookup->call = QV4::Lookup::Call::GetterGeneric;
         break;
     default:
@@ -2842,4 +2845,5 @@
                 ? writeBackFallbackAsVariant(lookup, object, source)
                 : writeBackFallbackProperty(lookup, object, source);
+        lookup->call = QV4::Lookup::Call::GetterGeneric;
         break;
     default:
@@ -3002,4 +3006,5 @@
                 ? storeFallbackAsVariant(engine->handle(), lookup, object, value)
                 : storeFallbackProperty(lookup, object, value);
+        lookup->call = QV4::Lookup::Call::SetterGeneric;
         break;
     default: