diff --git a/colossalai/tensor/padded_tensor/api.py b/colossalai/tensor/padded_tensor/api.py
index 5b66c016b399..d694ab08fc88 100644
--- a/colossalai/tensor/padded_tensor/api.py
+++ b/colossalai/tensor/padded_tensor/api.py
@@ -14,11 +14,13 @@ def _hijack_detach_and_clone(ptensor: torch.Tensor) -> torch.Tensor:
     ptensor._unpad_detach = ptensor.detach
     ptensor._unpad_clone = ptensor.clone
 
+    # the copies must be full padded tensors too, otherwise to_unpadded_tensor() fails on them
     def new_detach(self):
         t_ = self._unpad_detach()
         t_._padding_dim = self._padding_dim
         t_._origin_length = self._origin_length
         t_._current_length = self._current_length
+        _hijack_detach_and_clone(t_)
         return t_
 
     def new_clone(self, *args, **kwargs):
@@ -26,6 +28,7 @@ def new_clone(self, *args, **kwargs):
         t_._padding_dim = self._padding_dim
         t_._origin_length = self._origin_length
         t_._current_length = self._current_length
+        _hijack_detach_and_clone(t_)
         return t_
 
     # bind the new methods to the tensor
diff --git a/tests/test_checkpoint_io/test_gemini_checkpoint_io.py b/tests/test_checkpoint_io/test_gemini_checkpoint_io.py
index ba60de0bd1c1..3649b18ec8bb 100644
--- a/tests/test_checkpoint_io/test_gemini_checkpoint_io.py
+++ b/tests/test_checkpoint_io/test_gemini_checkpoint_io.py
@@ -23,7 +23,7 @@
 
 ASYNC_MODES = [False, True] if HAS_TENSORNVME else [False]
 try:
-    import apex.amp
+    pass
 
     APEX_AVAILABLE = True
 except ImportError:
diff --git a/tests/test_checkpoint_io/test_hybrid_parallel_plugin_checkpoint_io.py b/tests/test_checkpoint_io/test_hybrid_parallel_plugin_checkpoint_io.py
index fc464e7fa3e1..149ae0752779 100644
--- a/tests/test_checkpoint_io/test_hybrid_parallel_plugin_checkpoint_io.py
+++ b/tests/test_checkpoint_io/test_hybrid_parallel_plugin_checkpoint_io.py
@@ -1,8 +1,11 @@
+import glob
+
 import pytest
 import torch
 import torch.distributed as dist
 from packaging.version import Version
 from torch.optim import Adam
+from transformers import GPT2Config, GPT2LMHeadModel
 from utils import shared_tempdir
 
 import colossalai
@@ -146,9 +149,39 @@ def _preprocess_data(data):
     clear_layout_converter()
 
 
+@clear_cache_before_run()
+@parameterize("shard", [True, False])
+@parameterize("test_config", [{"tp_size": 1, "pp_size": 1}, {"tp_size": 1, "pp_size": 2, "num_microbatches": 2}])
+def exam_state_dict_padded_vocab(shard: bool, test_config: dict):
+    # a vocab size that is not a multiple of make_vocab_size_divisible_by (64), so the embedding and
+    # lm_head weights are padded tensors, which must be unpadded when saving (#6253)
+    config = GPT2Config(n_layer=2, n_head=4, n_embd=64, vocab_size=1000, n_positions=64)
+    booster = Booster(plugin=HybridParallelPlugin(**test_config, precision="fp16", initial_scale=1))
+    model = GPT2LMHeadModel(config).cuda()
+    model, *_ = booster.boost(model, Adam(model.parameters(), lr=1e-3))
+
+    with shared_tempdir() as tempdir:
+        model_ckpt_path = f"{tempdir}/model"
+        booster.save_model(model, model_ckpt_path, shard=shard)
+        dist.barrier()
+        if dist.get_rank() == 0:
+            # the checkpoint must hold the original (unpadded) vocab size
+            files = glob.glob(f"{model_ckpt_path}/*.bin") if shard else [model_ckpt_path]
+            saved = {}
+            for f in files:
+                saved.update(torch.load(f, map_location="cpu"))
+            assert saved["transformer.wte.weight"].shape == (config.vocab_size, config.n_embd)
+        new_model = GPT2LMHeadModel(config).cuda()
+        new_model, *_ = booster.boost(new_model, Adam(new_model.parameters(), lr=1e-3))
+        booster.load_model(new_model, model_ckpt_path)
+        check_state_dict_equal(model.unwrap().state_dict(), new_model.unwrap().state_dict())
+    dist.barrier()
+
+
 def run_dist(rank, world_size, port):
     colossalai.launch(rank=rank, world_size=world_size, host="localhost", port=port, backend="nccl")
     exam_state_dict()
+    exam_state_dict_padded_vocab()
 
 
 @pytest.mark.dist
diff --git a/tests/test_tensor/test_padded_tensor.py b/tests/test_tensor/test_padded_tensor.py
index 6d19845dff2f..a6062b93d281 100644
--- a/tests/test_tensor/test_padded_tensor.py
+++ b/tests/test_tensor/test_padded_tensor.py
@@ -36,6 +36,21 @@ def check_padded_tensor(rank, world_size, port):
     assert global_tensor.shape == original_tensor.shape
 
 
+def test_unpad_detached_and_cloned_tensor():
+    # detach() / clone() of a padded tensor must give a padded tensor that can be unpadded on its own,
+    # this is what checkpoint saving does before writing a parameter
+    original = torch.rand(10, 4)
+    padded = to_padded_tensor(original.clone(), current_length=16, padding_dim=0)
+    for tensor_copy in (padded.detach(), padded.clone(), padded.detach().clone()):
+        assert is_padded_tensor(tensor_copy)
+        assert tensor_copy.shape == (16, 4)
+        unpadded = to_unpadded_tensor(tensor_copy)
+        assert not is_padded_tensor(unpadded)
+        assert torch.equal(unpadded, original)
+    # the source tensor is still padded
+    assert is_padded_tensor(padded) and padded.shape == (16, 4)
+
+
 @rerun_if_address_is_in_use()
 def test_padded_tensor():
     world_size = 4
diff --git a/tests/test_zero/test_gemini/test_optim.py b/tests/test_zero/test_gemini/test_optim.py
index b89c591882d6..a0970e43db9e 100644
--- a/tests/test_zero/test_gemini/test_optim.py
+++ b/tests/test_zero/test_gemini/test_optim.py
@@ -15,7 +15,7 @@
 from tests.kit.model_zoo import model_zoo, run_fwd_bwd
 
 try:
-    import apex.amp
+    pass
 
     APEX_AMP_AVAILABLE = True
 except ImportError: