diff -r f24c30a19898 -r 4a23058e4d9f server/session.py
--- a/server/session.py	Thu Apr 24 17:52:20 2014 +0200
+++ b/server/session.py	Mon Apr 28 12:54:14 2014 +0200
@@ -593,6 +593,7 @@
             if new_cnxset is old_cnxset:
                 return #nothing to do
             if old_cnxset is not None:
+                old_cnxset.rollback()
                 self._cnxset = None
                 self.ctx_count -= 1
                 self._cnxset_tracker.forget(self.connectionid, old_cnxset)