--- a/hgext/evolve.py	Thu Mar 17 09:39:35 2016 -0700
+++ b/hgext/evolve.py	Thu Mar 17 10:04:30 2016 -0700
@@ -3838,6 +3838,14 @@
     bmdeactivate(repo)
     if keepbranch:
        repo.dirstate.setbranch(orig.branch())
+    if util.safehasattr(repo, 'currenttopic'):
+        # uurrgs
+        # there no other topic setter yet
+        if not orig.topic() and repo.vfs.exists('topic'):
+                repo.vfs.unlink('topic')
+        else:
+            with repo.vfs.open('topic', 'w') as f:
+                f.write(orig.topic())
 
     try:
        r = merge.graft(repo, orig, pctx, ['local', 'graft'], True)