diff -r a17033cfc892 -r 8dc44329f5c8 server/session.py
--- a/server/session.py	Mon Feb 08 21:22:10 2010 +0100
+++ b/server/session.py	Mon Feb 08 21:27:30 2010 +0100
@@ -485,7 +485,10 @@
                     for operation in processed:
                         operation.handle_event('revert%s_event' % trstate)
                     # res
-                    self.pending_operations[:] = processed + self.pending_operations
+
+                    # XXX self.pending_operations is supposed to be
+                    # read-only, and we are clearly modifying it here.
+                    self.pending_operations[:] = processed + self.pending_operations 
                     self.rollback(reset_pool)
                     raise
             self.pool.commit()