Workaround for incompatibility between Qt 5.5+ and Ubuntu that caused the context menu for the book list to flicker. Fixes #1534936 [Context menu of the individual books on Ubuntu 15:10 flawed](https://bugs.launchpad.net/calibre/+bug/1534936)

src/calibre/gui2/cover_flow.py

@@ -13,6 +13,7 @@ from PyQt5.Qt import (QImage, QSizePolicy, QTimer, QDialog, Qt, QSize, QAction,
         QStackedLayout, QLabel, QByteArray, pyqtSignal, QKeySequence, QFont)
 
 from calibre import plugins
+from calibre.constants import islinux
 from calibre.gui2 import (config, available_height, available_width, gprefs,
         rating_font)
 
@@ -170,8 +171,10 @@ if pictureflow is not None:
 
         def contextMenuEvent(self, event):
             if self.context_menu is not None:
+                from calibre.gui2.main_window import clone_menu
                 self.context_menu_requested.emit()
-                self.context_menu.popup(event.globalPos())
+                m = clone_menu(self.context_menu) if islinux else self.context_menu
+                m.popup(event.globalPos())
                 event.accept()
 
         def sizeHint(self):

src/calibre/gui2/library/views.py

@@ -15,6 +15,7 @@ from PyQt5.Qt import (
     QIcon, QItemSelection, QMimeData, QDrag, QStyle, QPoint, QUrl, QHeaderView,
     QStyleOptionHeader, QItemSelectionModel, QSize, QFontMetrics)
 
+from calibre.constants import islinux
 from calibre.gui2.library.delegates import (RatingDelegate, PubDateDelegate,
     TextDelegate, DateDelegate, CompleteDelegate, CcTextDelegate,
     CcBoolDelegate, CcCommentsDelegate, CcDateDelegate, CcTemplateDelegate,
@@ -818,11 +819,13 @@ class BooksView(QTableView):  # {{{
         self.edit_collections_action = edit_collections_action
 
     def contextMenuEvent(self, event):
+        from calibre.gui2.main_window import clone_menu
         sac = self.gui.iactions['Sort By']
         sort_added = tuple(ac for ac in self.context_menu.actions() if ac is sac.qaction)
         if sort_added:
             sac.update_menu()
-        self.context_menu.popup(event.globalPos())
+        m = clone_menu(self.context_menu) if islinux else self.context_menu
+        m.popup(event.globalPos())
         event.accept()
     # }}}
 

src/calibre/gui2/main_window.py

@@ -162,3 +162,29 @@ class MainWindow(QMainWindow):
         elif etype == ev.WindowUnblocked:
             self.window_unblocked.emit()
         return QMainWindow.event(self, ev)
+
+def clone_menu(menu):
+    def clone_action(ac, parent):
+        if ac.isSeparator():
+            ans = QAction(parent)
+            ans.setSeparator(True)
+            return ans
+        sc = ac.shortcut()
+        sc = '' if sc.isEmpty() else sc.toString(sc.NativeText)
+        ans = QAction(ac.icon(), ac.text() + '\t' + sc, parent)
+        ans.triggered.connect(ac.trigger)
+        ans.setEnabled(ac.isEnabled())
+        ans.setStatusTip(ac.statusTip())
+        ans.setVisible(ac.isVisible())
+        return ans
+
+    def clone_one_menu(m):
+        ans = QMenu(m.parent())
+        for ac in m.actions():
+            cac = clone_action(ac, ans)
+            ans.addAction(cac)
+            m = ac.menu()
+            if m is not None:
+                cac.setMenu(clone_menu(m))
+        return ans
+    return clone_one_menu(menu)