Pre-emptive fix of a bug. There is no way of producing the bug with the

theano/scan_module/scan_op.py

@@ -707,27 +707,44 @@ class Scan(Op):
         if not( type(scan_outputs) in (list,tuple)):
             scan_outputs = [scan_outputs]
         # 3. un-group / unzip the inputs
-        seqs   = self.inputs[:self.n_seqs]
+        # Note ! We don't want to use the actual same variable as the ones
+        # used by the original scan, rather create clones of them
+
+        def new_var(x):
+            nw_x = x.type()
+            if x.name:
+                nw_x.name=x.name +'grad_copy'
+            return nw_x
+
+
+        self_inputs = [new_var(x) for x in self.inputs ]
+        givens = {}
+        for new_x, x in zip(self_inputs, self.inputs):
+            givens[x] = new_x
+        self_outputs = scan_utils.clone(self.outputs, replace=givens)
+
+
+        seqs   = self_inputs[:self.n_seqs]
 
         offset        = self.n_seqs
         n_ins_mit_mot = numpy.sum([0] + [ len(self.tap_array[x]) for x
                                    in xrange(self.n_mit_mot) ])
-        outs_mit_mot  = self.inputs[offset:offset+n_ins_mit_mot]
+        outs_mit_mot  = self_inputs[offset:offset+n_ins_mit_mot]
 
         offset       += n_ins_mit_mot
         n_ins_mit_sot = numpy.sum([0] + [ len(self.tap_array[x]) for x
                                    in xrange( self.n_mit_mot
                                              , self.n_mit_mot+self.n_mit_sot)])
-        outs_mit_sot          = self.inputs[offset:offset+n_ins_mit_sot]
+        outs_mit_sot          = self_inputs[offset:offset+n_ins_mit_sot]
         offset               += n_ins_mit_sot
-        outs_sit_sot          = self.inputs[offset:offset+self.n_sit_sot]
+        outs_sit_sot          = self_inputs[offset:offset+self.n_sit_sot]
         offset               += self.n_sit_sot
-        old_scan_shared_ins   = self.inputs[offset:offset+self.n_shared_outs]
+        old_scan_shared_ins   = self_inputs[offset:offset+self.n_shared_outs]
         out_offset            = ( self.n_mit_mot_outs
                                  + self.n_mit_sot
                                  + self.n_nit_sot
                                  + self.n_sit_sot )
-        old_scan_shared_outs  = self.outputs[out_offset:]
+        old_scan_shared_outs  = self_outputs[out_offset:]
         arg_offset = ( 1
                       + self.n_seqs
                       + self.n_mit_mot
@@ -735,7 +752,7 @@ class Scan(Op):
                       + self.n_sit_sot)
         old_scan_init = args[arg_offset: arg_offset+self.n_shared_outs]
         offset       += self.n_shared_outs
-        other_args    = self.inputs[offset:]
+        other_args    = self_inputs[offset:]
 
 
         # 4. Collect (possibly) differentiable inputs
@@ -758,7 +775,7 @@ class Scan(Op):
                + self.n_mit_sot
                + self.n_sit_sot
                + self.n_nit_sot )
-        clean_outputs    = self.outputs[:end]
+        clean_outputs    = self_outputs[:end]
         g_outs_no_shared = g_outs[:end]
 
         # 7.1. empty lists to hold gradients
@@ -1016,7 +1033,7 @@ class Scan(Op):
                   + self.n_sit_sot
                   + self.n_shared_outs )
 
-        inner_other_args = self.inputs[offset:]
+        inner_other_args = self_inputs[offset:]
         inner_gfn_ins  = ( inner_seqs         +
                           inner_mit_mot       +
                           scan_shared_ins     +