fix gh-1344. Scan opt error/warning.

theano/scan_module/scan_opt.py

@@ -506,7 +506,7 @@ class PushOutSeqScan(gof.Optimizer):
                     replace_with[x] = y
 
             # We need to add one extra dimension to the outputs
-            if replace_with:
+            if replace_with and len(replace_with) == len(node.outputs):
                 fgraph.replace_all_validate_remove(
                     replace_with.items(),
                     remove=[node],

theano/scan_module/tests/test_scan.py

@@ -2739,6 +2739,26 @@ class T_Scan(unittest.TestCase):
         assert len([x for x in scan_node.op.fn.maker.fgraph.toposort()
                     if isinstance(x.op, theano.tensor.Elemwise)]) == 0
 
+    def test_pushout_nomodif(self):
+        inp = tensor.matrix('inp')
+
+        def fn(i, i_tm1):
+            return i + 10, i_tm1
+
+        ([i_t, i_tm1], _) = theano.scan(
+            fn, sequences=[inp],
+            outputs_info=[numpy.asarray([0.0, 0.0], theano.config.floatX),
+                          None])
+        f = theano.function([inp], [i_t, i_tm1])
+        val = numpy.arange(10).reshape(5, 2)
+        ret = f(val)
+        utt.assert_allclose(ret[0], val+10)
+        utt.assert_allclose(ret[1], [[0.,  0.],
+                                     [10., 11.],
+                                     [12., 13.],
+                                     [14., 15.],
+                                     [16., 17.]])
+
     def test_alloc_inputs1(self):
         W1 = tensor.matrix('W1')
         W2 = tensor.matrix('W2')