--- a/hgext3rd/topic/__init__.py	Fri Jun 23 10:21:37 2017 +0200
+++ b/hgext3rd/topic/__init__.py	Thu Jun 22 09:48:40 2017 +0200
@@ -115,7 +115,9 @@
 
 testedwith = '4.0.2 4.1.3 4.2'
 
-def _contexttopic(self):
+def _contexttopic(self, force=False):
+    if not (force or self.mutable()):
+        return ''
     return self.extra().get(constants.extrakey, '')
 context.basectx.topic = _contexttopic