The key event should be stopped propagation when it's been processed as an accelerator.

ui/views/mus/native_widget_mus.cc

Index: ui/views/mus/native_widget_mus.cc
diff --git a/ui/views/mus/native_widget_mus.cc b/ui/views/mus/native_widget_mus.cc
index 111a32ef8e9da4a71a54a6022b429d92cfb260b5..3905e17d0363669b7a741f1cb9a8d65f30aa4b9d 100644
--- a/ui/views/mus/native_widget_mus.cc
+++ b/ui/views/mus/native_widget_mus.cc
@@ -821,12 +821,6 @@ void NativeWidgetMus::OnKeyEvent(ui::KeyEvent* event) {
     return;
 
   native_widget_delegate_->OnKeyEvent(event);
-  if (event->handled())
-    return;
-
-  if (GetWidget()->HasFocusManager() &&
-      !GetWidget()->GetFocusManager()->OnKeyEvent(*event))
-    event->SetHandled();
 }
 
 void NativeWidgetMus::OnMouseEvent(ui::MouseEvent* event) {