due to suspected instability with persistance Worker (randomly not persisted...

due to suspected instability with persistance Worker (randomly not persisted scenes, very hard to reproduce), switched to 'immediateSave mode' (at least for now)

src/core/UBPersistenceManager.h

@@ -77,7 +77,7 @@ class UBPersistenceManager : public QObject
         virtual void duplicateDocumentScene(UBDocumentProxy* pDocumentProxy, int index);
 
         virtual void persistDocumentScene(UBDocumentProxy* pDocumentProxy,
-                UBGraphicsScene* pScene, const int pSceneIndex, bool isAnAutomaticBackup = false, bool forceImmediateSaving = false);
+                UBGraphicsScene* pScene, const int pSceneIndex, bool isAnAutomaticBackup = false, bool forceImmediateSaving = true);
 
         virtual UBGraphicsScene* createDocumentSceneAt(UBDocumentProxy* pDocumentProxy, int index, bool useUndoRedoStack = true);