Ticket #15006: macgui-menu-corruption.txt

diff --git a/graphics/macgui/macwindowmanager.cpp b/graphics/macgui/macwindowmanager.cpp
index 3d333839b6b..41de14620fb 100644
--- a/graphics/macgui/macwindowmanager.cpp
+++ b/graphics/macgui/macwindowmanager.cpp
@@ -177,6 +177,8 @@ MacWindowManager::MacWindowManager(uint32 mode, MacPatterns *patterns, Common::L
        _menuDelay = 0;
        _menuTimerActive = false;
 
+       _activateScreenCopy = false;
+
        _engineP = nullptr;
        _engineR = nullptr;
        _redrawEngineCallback = nullptr;
@@ -447,14 +449,14 @@ void MacWindowManager::activateMenu() {
                return;
 
        if (_mode & kWMModalMenuMode) {
-               activateScreenCopy();
+               _activateScreenCopy = true;
        }
 
        _menu->setVisible(true);
 }
 
 void MacWindowManager::activateScreenCopy() {
-       Common::StackLock lock(_mutex);
+       // This is only called when the _mutex is already held
 
        if (_screen) {
                if (!_screenCopy)
@@ -897,6 +899,11 @@ void MacWindowManager::drawDesktop() {
 void MacWindowManager::draw() {
        Common::StackLock lock(_mutex);
 
+       if (_activateScreenCopy) {
+               _activateScreenCopy = false;
+               activateScreenCopy();
+       }
+
        removeMarked();
 
        Common::Rect bounds = getScreenBounds();
diff --git a/graphics/macgui/macwindowmanager.h b/graphics/macgui/macwindowmanager.h
index 22a128c77a0..feeb3a7ca98 100644
--- a/graphics/macgui/macwindowmanager.h
+++ b/graphics/macgui/macwindowmanager.h
@@ -457,6 +457,8 @@ private:
        MacMenu *_menu;
        uint32 _menuDelay;
 
+       bool _activateScreenCopy;
+
        Engine *_engineP;
        void *_engineR;
        void (*_redrawEngineCallback)(void *engine);