diff --git a/lark/parsers/earley.py b/lark/parsers/earley.py
index 0722fec..3c04ac1 100644
--- a/lark/parsers/earley.py
+++ b/lark/parsers/earley.py
@@ -110,8 +110,9 @@ class Column:
 
             if item.is_complete:
                 # XXX Potential bug: What happens if there's ambiguity in an empty rule?
-                if item.rule.expansion and item in self.completed:
-                    old_tree = self.completed[item].tree
+                item_key = item, item.tree  # Elsewhere, tree is not part of the comparison
+                if item.rule.expansion and item_key in self.completed:
+                    old_tree = self.completed[item_key].tree
                     if old_tree == item.tree:
                         is_empty = len(self.FIRST[item.rule.origin])
                         if is_empty:
@@ -130,7 +131,7 @@ class Column:
                         old_tree.children.append(item.tree)
                     # old_tree.children.append(item.tree)
                 else:
-                    self.completed[item] = item
+                    self.completed[item_key] = item
                 self.to_reduce.append(item)
             else:
                 if isinstance(item.expect, Terminal):
diff --git a/lark/parsers/xearley.py b/lark/parsers/xearley.py
index 9f30b23..693e54f 100644
--- a/lark/parsers/xearley.py
+++ b/lark/parsers/xearley.py
@@ -51,7 +51,7 @@ class Parser:
     def parse(self, stream, start_symbol=None):
         # Define parser functions
         start_symbol = start_symbol or self.start_symbol
-        delayed_matches = defaultdict(set)
+        delayed_matches = defaultdict(list)
         match_after_ignore = set()
 
         text_line = 1
@@ -88,7 +88,7 @@ class Parser:
             for x in self.ignore:
                 m = x.match(stream, i)
                 if m:
-                    delayed_matches[m.end()] |= set(to_scan)
+                    delayed_matches[m.end()] += set(to_scan)
                     if m.end() == len(stream):
                         match_after_ignore.update(set(column.to_reduce))
 
@@ -103,13 +103,13 @@ class Parser:
                 m = item.expect.match(stream, i)
                 if m:
                     t = Token(item.expect.name, m.group(0), i, text_line, text_column)
-                    delayed_matches[m.end()].add(item.advance(t))
+                    delayed_matches[m.end()].append(item.advance(t))
 
                     s = m.group(0)
                     for j in range(1, len(s)):
                         m = item.expect.match(s[:-j])
                         if m:
-                            delayed_matches[m.end()].add(item.advance(m.group(0)))
+                            delayed_matches[m.end()].append(item.advance(m.group(0)))
 
             next_set = Column(i+1, self.FIRST)
             next_set.add(delayed_matches[i+1])