Match broadcastable pattern of original variable

theano/scan_module/scan_utils.py

@@ -401,6 +401,12 @@ def expand(tensor_var, size):
     zeros_shape = [size + shapes[0]] + shapes[1:]
     empty = tensor.zeros(zeros_shape,
                                dtype=tensor_var.dtype)
+
+    # Make sure to reuse the broadcast pattern of the original tensor for
+    # every dimension but the first one.
+    broadcastable = (False,) + tensor_var.broadcastable[1:]
+    empty = tensor.patternbroadcast(empty, broadcastable)
+
     return tensor.set_subtensor(empty[:shapes[0]], tensor_var)