Gui: issue #8939: timers are moved between non-QThreads

src/Gui/Tree.cpp

@@ -3002,6 +3002,12 @@ void TreeWidget::onSelectTimer() {
 
 void TreeWidget::onSelectionChanged(const SelectionChanges& msg)
 {
+    // When running from a different thread Qt will raise a warning
+    // when trying to start the QTimer
+    if (Q_UNLIKELY(thread() != QThread::currentThread())) {
+        return;
+    }
+
     switch (msg.Type)
     {
     case SelectionChanges::AddSelection: