Merge branch 'master' into qt6_cmake_joshua

sources/ui/projectpropertiesdialog.cpp

@@ -63,7 +63,13 @@ ProjectPropertiesDialog::~ProjectPropertiesDialog ()
 */
 void ProjectPropertiesDialog::exec()
 {
-	m_properties_dialog->setWindowModality(Qt::WindowModal);
+	// ApplicationModal (not WindowModal) so no other window — including other
+	// MDI subwindows — can dispatch events while the dialog holds raw
+	// QETProject* pointers in its config pages.  WindowModal only blocks the
+	// parent ProjectView; the rest of the MDI area stays live, which allowed
+	// new_project / close_project to replace the project under the dialog
+	// and cause a SIGSEGV.  See issue #527.
+	m_properties_dialog->setWindowModality(Qt::ApplicationModal);
 	m_properties_dialog -> exec();
 }