next attempt to fix up postprocessing

src/fpylll/algorithms/bkz.py

@@ -188,6 +188,9 @@ def svp_postprocessing(self, kappa, block_size, solution, tracer):
         :param tracer: object for maintaining statistics
 
         :returns: ``True`` if no change was made and ``False`` otherwise
+
+        ..  note :: postprocessing does not necessarily leave the GSO in a safe state.  You may
+            need to call ``update_gso()`` afterwards.
         """
         if solution is None:
             return True
@@ -253,9 +256,6 @@ def svp_postprocessing(self, kappa, block_size, solution, tracer):
 
             self.M.move_row(kappa + block_size - 1, kappa)
 
-        # TODO the C++ version doesn't seem to require this call
-        self.lll_obj.size_reduction(kappa, kappa+block_size, kappa)
-
         return False
 
     def svp_reduction(self, kappa, block_size, params, tracer=dummy_tracer):

src/fpylll/algorithms/bkz2.py

@@ -70,6 +70,10 @@ def svp_preprocessing(self, kappa, block_size, param, tracer=dummy_tracer):
             prepar = param.__class__(block_size=preproc, strategies=param.strategies, flags=BKZ.GH_BND)
             clean &= self.tour(prepar, kappa, kappa + block_size, tracer=tracer)
 
+        # clean up the GSO which is left in a messy state by postprocessing
+        # TODO the C++ version doesn't seem to require this call
+        self.lll_obj.size_reduction(kappa, kappa+block_size, kappa)
+
         return clean
 
     def svp_reduction(self, kappa, block_size, param, tracer=dummy_tracer):