safe_new should return a variable not a graph

theano/scan_module/scan_utils.py

@@ -48,7 +48,10 @@ def safe_new(x, tag='', dtype=None):
         nw_name = None
     if isinstance(x, theano.Constant):
         if dtype and x.dtype != dtype:
-            return x.clone().astype(dtype)
+            casted_x = x.astype(dtype)
+            nwx = x.__class__(casted_x.type, x.data, x.name)
+            nwx.tag = copy(x.tag)
+            return nwx
         else:
             return x.clone()
     # Note, as_tensor_variable will convert the Scalar into a
@@ -70,6 +73,8 @@ def safe_new(x, tag='', dtype=None):
             # ndarrays
             pass
     nw_x = x.type()
+    if dtype and nw_x.dtype != dtype:
+        nw_x = nw_x.astype(dtype).type()
     nw_x.name = nw_name
     # Preserve test values so that the 'compute_test_value' option can be used.
     # The test value is deep-copied to ensure there can be no interactions
@@ -82,9 +87,6 @@ def safe_new(x, tag='', dtype=None):
             # This means `x` has no test value.
             pass
 
-    if dtype and nw_x.dtype != dtype:
-        nw_x = nw_x.astype(dtype)
-
     return nw_x