diff --git a/python/singa/module.py b/python/singa/module.py
index 23e1715c77..88881c0b1d 100644
--- a/python/singa/module.py
+++ b/python/singa/module.py
@@ -48,7 +48,11 @@ def wrapper(self, *args, **kwargs):
                     # deconstruct Operations before running the entire graph
                     if name == 'optim':
                         for fname in self._results:
-                            self._results[fname].creator = None
+                            if isinstance(self._results[fname], list):
+                                for _matrix in self._results[fname]:
+                                    _matrix.creator = None
+                            else:
+                                self._results[fname].creator = None
                         # make sure all Operations are deallocated
                         gc.collect()
                     # add result tensor
diff --git a/src/core/scheduler/scheduler.cc b/src/core/scheduler/scheduler.cc
index 76b9e7f308..be31c6ecc6 100644
--- a/src/core/scheduler/scheduler.cc
+++ b/src/core/scheduler/scheduler.cc
@@ -189,7 +189,8 @@ void Graph::Debug() {
   for (auto it : blkInfos) {
     auto blkInfo = it;
     ss << "Block[" << std::setw(w) << blkInfo->id_ << "] addr[" << std::setw(w)
-       << blkInfo->blk_ << "] graph_ref[" << std::setw(w) << blkInfo->graph_ref_
+       << blkInfo->blk_ << "] size[" << std::setw(10) << blkInfo->blk_->size()
+       << "] graph_ref[" << std::setw(w) << blkInfo->graph_ref_
        << "] ref_count[" << std::setw(w) << blkInfo->blk_->ref_count() << "] ";
     switch (blkInfo->type_) {
       case BlockType::kInput: