[TD]fix lost parent on undo

src/Mod/TechDraw/Gui/MDIViewPage.cpp

@@ -76,7 +76,6 @@
 #include "Rez.h"
 #include "ViewProviderPage.h"
 
-
 using namespace TechDrawGui;
 using namespace TechDraw;
 namespace bp = boost::placeholders;
@@ -194,6 +193,7 @@ bool MDIViewPage::onMsg(const char* pMsg, const char**)
     else if (strcmp("Undo", pMsg) == 0) {
         doc->undo(1);
         Gui::Command::updateActive();
+        fixSceneDependencies();    // check QGraphicsScene item parenting
         return true;
     }
     else if (strcmp("Redo", pMsg) == 0) {
@@ -246,6 +246,14 @@ void MDIViewPage::setTabText(std::string tabText)
     }
 }
 
+// advise the page to check QGraphicsScene parent/child relationships after undo
+void MDIViewPage::fixSceneDependencies()
+{
+    if (getViewProviderPage()) {
+        getViewProviderPage()->fixSceneDependencies();
+    }
+}
+
 //**** printing routines
 
 void MDIViewPage::getPaperAttributes()