QQmlPropertyBinding: Do re-attach observer after handling undefined

As noted in the comments above, we need to restore the binding to its
original state after resetting the property. This includes re-adding any
observers.

Pick-to: 6.2 6.5 6.6
Fixes: QTBUG-114874
Change-Id: I2113a59f1bed59753c77ca3e0b00fed4c0487584
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/src/qml/qml/qqmlpropertybinding.cpp b/src/qml/qml/qqmlpropertybinding.cpp
index 6ec84d67d4..d1c44f205d 100644
--- a/src/qml/qml/qqmlpropertybinding.cpp
+++ b/src/qml/qml/qqmlpropertybinding.cpp
@@ -251,8 +251,10 @@ void QQmlPropertyBinding::handleUndefinedAssignment(QQmlEnginePrivate *ep, void
         // reset might have changed observers (?), so refresh firstObserver
         firstObserver = bindingDataPointer.firstObserver();
         bindingData->d_ref() = reinterpret_cast<quintptr>(this) | QtPrivate::QPropertyBindingData::BindingBit;
-        if (firstObserver)
+        if (firstObserver) {
             bindingDataPointer.setObservers(firstObserver.ptr);
+            prependObserver(firstObserver);
+        }
     } else {
         QQmlError qmlError;
         auto location = jsExpression()->sourceLocation();