diff --git a/spacy/tokens/span.pyx b/spacy/tokens/span.pyx
index 1c316c8ea..c04edba6a 100644
--- a/spacy/tokens/span.pyx
+++ b/spacy/tokens/span.pyx
@@ -280,12 +280,14 @@ cdef class Span:
                     end = key[3]
                     if start is not None or end is not None:
                         start -= char_offset
+                        # Check if Span object
                         if end is not None:
                             end -= char_offset
                             _label = key[4]
                             _kb_id = key[5]
                             _span_id = key[6]
                             user_data[(data_type, name, start, end, _label, _kb_id, _span_id)] = copy.copy(value)
+                        # Else Token object
                         else:
                             user_data[(data_type, name, start, end)] = copy.copy(value)
                 else:
@@ -804,8 +806,6 @@ cdef class Span:
                 new = Underscore(Underscore.span_extensions, self, start=self.span_c().start_char, end=self.span_c().end_char, label=self.label, kb_id=self.kb_id, span_id=self.id)
                 old = Underscore(Underscore.span_extensions, self, start=self.span_c().start_char, end=self.span_c().end_char, label=old_label, kb_id=self.kb_id, span_id=self.id)
                 Underscore._replace_keys(old, new)
-            else:
-                self.span_c().label = label
 
     property kb_id:
         def __get__(self):
@@ -818,8 +818,6 @@ cdef class Span:
                 new = Underscore(Underscore.span_extensions, self, start=self.span_c().start_char, end=self.span_c().end_char, label=self.label, kb_id=self.kb_id, span_id=self.id)
                 old = Underscore(Underscore.span_extensions, self, start=self.span_c().start_char, end=self.span_c().end_char, label=self.label, kb_id=old_kb_id, span_id=self.id)
                 Underscore._replace_keys(old, new)
-            else:
-                self.span_c().kb_id = kb_id
 
     property id:
         def __get__(self):
@@ -832,8 +830,6 @@ cdef class Span:
                 new = Underscore(Underscore.span_extensions, self, start=self.span_c().start_char, end=self.span_c().end_char, label=self.label, kb_id=self.kb_id, span_id=self.id)
                 old = Underscore(Underscore.span_extensions, self, start=self.span_c().start_char, end=self.span_c().end_char, label=self.label, kb_id=self.kb_id, span_id=old_id)
                 Underscore._replace_keys(old, new)
-            else:
-                self.span_c().id = id
 
     property ent_id:
         """Alias for the span's ID."""
diff --git a/spacy/tokens/underscore.py b/spacy/tokens/underscore.py
index bbdd409b2..f2f357441 100644
--- a/spacy/tokens/underscore.py
+++ b/spacy/tokens/underscore.py
@@ -122,8 +122,9 @@ class Underscore:
         """
         for name in old_underscore._extensions:
             old_key = old_underscore._get_key(name)
+            old_doc = old_underscore._doc
             new_key = new_underscore._get_key(name)
-            if old_key in old_underscore._doc.user_data and old_key != new_key:
+            if old_key != new_key and old_key in old_doc.user_data:
                 old_underscore._doc.user_data[
                     new_key
                 ] = old_underscore._doc.user_data.pop(old_key)