Keep the most recent stack trace, not the oldest

theano/gof/utils.py

@@ -87,8 +87,10 @@ def add_tag_trace(thing, user_line=1):
                 break
         if not rm:
             break
+    # Keep only the most recent stack level.
+    # The order is from the oldest to the newest
     if len(tr) > user_line:
-        tr = tr[:user_line]
+        tr = tr[-user_line:]
     thing.tag.trace = tr
     return thing