diff --git a/masque/library.py b/masque/library.py
index 99a43f5..5e5c80a 100644
--- a/masque/library.py
+++ b/masque/library.py
@@ -235,8 +235,12 @@ class Library(Mapping[str, 'Pattern'], metaclass=ABCMeta):
 
                 if target not in flattened:
                     flatten_single(target)
-                if flattened[target] is None:
+
+                target_pat = flattened[target]
+                if target_pat is None:
                     raise PatternError(f'Circular reference in {name} to {target}')
+                if target_pat.is_empty()        # avoid some extra allocations
+                    continue
 
                 p = ref.as_pattern(pattern=flattened[target])
                 if not flatten_ports:
@@ -613,8 +617,8 @@ class MutableLibrary(Library, MutableMapping[str, 'Pattern'], metaclass=ABCMeta)
             raise LibraryError('Received a non-Tree library containing multiple cells')
 
         name = next(iter(other))
-        self.add(other)
-        return name
+        rename_map = self.add(other)
+        return rename_map.get(name, name)
 
     def dedup(
             self: ML,
diff --git a/masque/pattern.py b/masque/pattern.py
index c9d40fb..055f6e2 100644
--- a/masque/pattern.py
+++ b/masque/pattern.py
@@ -521,6 +521,7 @@ class Pattern(PortList, AnnotatableImpl, Mirrorable):
 
     def is_empty(self) -> bool:
         """
+        # TODO is_empty doesn't include ports... maybe there should be an equivalent?
         Returns:
             True if the pattern is contains no shapes, labels, or refs.
         """
@@ -575,6 +576,7 @@ class Pattern(PortList, AnnotatableImpl, Mirrorable):
         """
         flattened: Dict[Optional[str], Optional[P]] = {}
 
+        # TODO both Library and Pattern have flatten()... pattern is in-place?
         def flatten_single(name: Optional[str]) -> None:
             if name is None:
                 pat = self
@@ -589,8 +591,12 @@ class Pattern(PortList, AnnotatableImpl, Mirrorable):
 
                 if target not in flattened:
                     flatten_single(target)
-                if flattened[target] is None:
+
+                target_pat = flattened[target]
+                if target_pat is None:
                     raise PatternError(f'Circular reference in {name} to {target}')
+                if target_pat.is_empty()        # avoid some extra allocations
+                    continue
 
                 p = ref.as_pattern(pattern=flattened[target])
                 if not flatten_ports:
diff --git a/masque/ref.py b/masque/ref.py
index 37cd696..7b699cc 100644
--- a/masque/ref.py
+++ b/masque/ref.py
@@ -200,6 +200,9 @@ class Ref(
             return None
         if library is not None and self.target not in library:
             raise PatternError(f'get_bounds() called on dangling reference to "{self.target}"')
+        if pattern is not None and pattern.is_empty():
+            # no need to run as_pattern()
+            return None
         return self.as_pattern(pattern=pattern, library=library).get_bounds(library)
 
     def __repr__(self) -> str: