diff --git a/toolkit.py b/toolkit.py
index c941dd0decfe64feb0093be5178e0fb0761642e1..5fd767425e5fff17aea994b7ce47a86aae3817e0 100755
--- a/toolkit.py
+++ b/toolkit.py
@@ -383,6 +383,8 @@ class ClassificationProject(object):
 
     def _load_data(self):
 
+        self._w_train_tot = None
+
         try:
 
             # if those don't exist, we need to load them from ROOT trees first
@@ -1142,11 +1144,11 @@ class ClassificationProject(object):
         sig = self.w_train_tot[self.y_train == 1]
         ax.hist(bkg, bins=bins, range=range, color="b", alpha=0.5)
         ax.set_yscale("log")
-        return save_show(plt, fig, os.path.join(self.project_dir, "eventweights_bkg.pdf"))
+        save_show(plt, fig, os.path.join(self.project_dir, "eventweights_bkg.pdf"))
         fig, ax = plt.subplots()
         ax.hist(sig, bins=bins, range=range, color="r", alpha=0.5)
         ax.set_yscale("log")
-        return save_show(plt, fig, os.path.join(self.project_dir, "eventweights_sig.pdf"))
+        save_show(plt, fig, os.path.join(self.project_dir, "eventweights_sig.pdf"))
 
 
     def plot_ROC(self, xlim=(0,1), ylim=(0,1)):
@@ -1612,6 +1614,7 @@ class ClassificationProjectDataFrame(ClassificationProject):
             self._y_test = None
             self._w_train = None
             self._w_test = None
+            self._w_train_tot = None
 
         if not self.data_transformed:
             self._transform_data()