diff --git a/.github/workflows/benchmark.yml b/.github/workflows/benchmark.yml
index 34898e640697..49ef91de9be4 100644
--- a/.github/workflows/benchmark.yml
+++ b/.github/workflows/benchmark.yml
@@ -114,7 +114,7 @@ jobs:
               const previousSizeMB = previousSize !== 'Unknown' ? (previousSize / 1024 / 1024).toFixed(4) : 'Unknown';
               const currentSizeMB = currentSize !== 'Unknown' ? (currentSize / 1024 / 1024).toFixed(4) : 'Unknown';
 
-              let commentBody = `The previous wheel size was **${previousSizeMB} MB**.\nThe current wheel size after this PR is **${currentSizeMB} MB**.`;
+              let commentBody = `The uncompressed binary size was **${previousSizeMB} MB**.\nThe uncompressed binary size after this PR is **${currentSizeMB} MB**.`;
 
               // Calculate percentage increase if both sizes are available
               if (previousSize !== 'Unknown' && currentSize !== '') {
diff --git a/crates/polars-core/src/chunked_array/comparison/categorical.rs b/crates/polars-core/src/chunked_array/comparison/categorical.rs
index bbcd6b6047c9..09573c5fbd32 100644
--- a/crates/polars-core/src/chunked_array/comparison/categorical.rs
+++ b/crates/polars-core/src/chunked_array/comparison/categorical.rs
@@ -374,13 +374,29 @@ where
         // Apply comparison on categories map and then do a lookup
         let bitmap = str_single_compare_function(lhs.get_rev_map().get_categories(), rhs);
 
-        Ok(
-            BooleanChunked::from_iter_trusted_length(lhs.physical().into_iter().map(|opt_idx| {
-                // SAFETY: indexing into bitmap with same length as original array
-                opt_idx.map(|idx| unsafe { bitmap.get_bit_unchecked(idx as usize) })
-            }))
-            .with_name(lhs.name().clone()),
-        )
+        let mask = match lhs.get_rev_map().as_ref() {
+            RevMapping::Local(_, _) => {
+                BooleanChunked::from_iter_trusted_length(lhs.physical().into_iter().map(
+                    |opt_idx| {
+                        // SAFETY: indexing into bitmap with same length as original array
+                        opt_idx.map(|idx| unsafe { bitmap.get_bit_unchecked(idx as usize) })
+                    },
+                ))
+            },
+            RevMapping::Global(idx_map, _, _) => {
+                BooleanChunked::from_iter_trusted_length(lhs.physical().into_iter().map(
+                    |opt_idx| {
+                        // SAFETY: indexing into bitmap with same length as original array
+                        opt_idx.map(|idx| unsafe {
+                            let idx = *idx_map.get(&idx).unwrap();
+                            bitmap.get_bit_unchecked(idx as usize)
+                        })
+                    },
+                ))
+            },
+        };
+
+        Ok(mask.with_name(lhs.name().clone()))
     }
 }
 
diff --git a/crates/polars-core/src/chunked_array/logical/categorical/ops/unique.rs b/crates/polars-core/src/chunked_array/logical/categorical/ops/unique.rs
index c46291e4382a..17752f828d8d 100644
--- a/crates/polars-core/src/chunked_array/logical/categorical/ops/unique.rs
+++ b/crates/polars-core/src/chunked_array/logical/categorical/ops/unique.rs
@@ -1,5 +1,3 @@
-use polars_compute::unique::{DictionaryRangedUniqueState, RangedUniqueKernel};
-
 use super::*;
 
 impl CategoricalChunked {
@@ -41,18 +39,7 @@ impl CategoricalChunked {
                 Ok(out)
             }
         } else {
-            let mut state = DictionaryRangedUniqueState::new(cat_map.get_categories().to_boxed());
-            for chunk in self.physical().downcast_iter() {
-                state.key_state().append(chunk);
-            }
-            let (_, unique, _) = state.finalize_unique().take();
-            let ca = unsafe {
-                UInt32Chunked::from_chunks_and_dtype_unchecked(
-                    self.physical().name().clone(),
-                    vec![unique.to_boxed()],
-                    DataType::UInt32,
-                )
-            };
+            let ca = self.physical().unique()?;
             // SAFETY:
             // we only removed some indexes so we are still in bounds
             unsafe {
@@ -70,12 +57,7 @@ impl CategoricalChunked {
         if self._can_fast_unique() {
             Ok(self.get_rev_map().len())
         } else {
-            let cat_map = self.get_rev_map();
-            let mut state = DictionaryRangedUniqueState::new(cat_map.get_categories().to_boxed());
-            for chunk in self.physical().downcast_iter() {
-                state.key_state().append(chunk);
-            }
-            Ok(state.finalize_n_unique())
+            self.physical().n_unique()
         }
     }
 
diff --git a/py-polars/tests/unit/datatypes/test_categorical.py b/py-polars/tests/unit/datatypes/test_categorical.py
index 66aa7b2ba898..d5416bc47a93 100644
--- a/py-polars/tests/unit/datatypes/test_categorical.py
+++ b/py-polars/tests/unit/datatypes/test_categorical.py
@@ -904,7 +904,7 @@ def test_perfect_group_by_19950() -> None:
 def test_categorical_unique() -> None:
     s = pl.Series(["a", "b", None], dtype=pl.Categorical)
     assert s.n_unique() == 3
-    assert s.unique().to_list() == ["a", "b", None]
+    assert s.unique().sort().to_list() == [None, "a", "b"]
 
 
 @StringCache()
@@ -925,3 +925,22 @@ def test_categorical_unique_20539() -> None:
         "unique": [["a", "b"], ["b", "c"], ["c"]],
         "unique_with_order": [["a", "b"], ["b", "c"], ["c"]],
     }
+
+
+@StringCache()
+@pytest.mark.may_fail_auto_streaming
+def test_categorical_prefill() -> None:
+    # https://github.com/pola-rs/polars/pull/20547#issuecomment-2569473443
+    # prefill cache
+    pl.Series(["aaa", "bbb", "ccc"], dtype=pl.Categorical)  # pre-fill cache
+
+    # test_compare_categorical_single
+    assert (pl.Series(["a"], dtype=pl.Categorical) < "a").to_list() == [False]
+
+    # test_unique_categorical
+    a = pl.Series(["a"], dtype=pl.Categorical)
+    assert a.unique().to_list() == ["a"]
+
+    s = pl.Series(["1", "2", "3"], dtype=pl.Categorical)
+    s = s.filter([True, False, True])
+    assert s.n_unique() == 2