diff --git a/python/sglang/srt/managers/schedule_batch.py b/python/sglang/srt/managers/schedule_batch.py
index d5e85b986..05b6ba059 100755
--- a/python/sglang/srt/managers/schedule_batch.py
+++ b/python/sglang/srt/managers/schedule_batch.py
@@ -3345,6 +3345,10 @@ class ScheduleBatch(ScheduleBatchDisaggregationDecodeMixin):
         # prefill-time tensor so it doesn't leak into ForwardBatch.
         self.input_embeds = None
 
+        self.mamba_cow_src_indices = None
+        self.mamba_cow_dst_indices = None
+        self.mamba_clear_indices = None
+
         # Clear context parallel metadata - CP is only for prefill, not decode
         if hasattr(self, "attn_cp_metadata") and self.attn_cp_metadata is not None:
             self.attn_cp_metadata = None
diff --git a/test/registered/unit/managers/test_schedule_batch_prepare_for_decode.py b/test/registered/unit/managers/test_schedule_batch_prepare_for_decode.py
index 4c3df0a42..ca47ad700 100644
--- a/test/registered/unit/managers/test_schedule_batch_prepare_for_decode.py
+++ b/test/registered/unit/managers/test_schedule_batch_prepare_for_decode.py
@@ -6,7 +6,7 @@ import torch
 
 from sglang.srt.runtime_context import get_context
 from sglang.test.ci.ci_register import register_cpu_ci
-from sglang.test.test_utils import maybe_stub_sgl_kernel
+from sglang.test.test_utils import CustomTestCase, maybe_stub_sgl_kernel
 
 maybe_stub_sgl_kernel()
 
@@ -39,6 +39,25 @@ def _make_decode_batch():
     return batch
 
 
+class TestPrepareForDecodeMambaInit(CustomTestCase):
+    def test_spec_decode_drops_extend_mamba_init_metadata(self):
+        batch = ScheduleBatch(reqs=[])
+        batch.spec_algorithm = types.SimpleNamespace(is_none=lambda: False)
+        batch.mamba_cow_src_indices = torch.tensor([1])
+        batch.mamba_cow_dst_indices = torch.tensor([2])
+        batch.mamba_clear_indices = torch.tensor([3])
+
+        with patch(
+            "sglang.srt.speculative.spec_utils.spec_prepare_for_decode"
+        ) as prepare:
+            batch.prepare_for_decode()
+
+        prepare.assert_called_once_with(batch)
+        self.assertIsNone(batch.mamba_cow_src_indices)
+        self.assertIsNone(batch.mamba_cow_dst_indices)
+        self.assertIsNone(batch.mamba_clear_indices)
+
+
 class TestPrepareForDecodeSeqLensOwnership(unittest.TestCase):
     def test_decode_seq_lens_bump_is_out_of_place(self):
         """Each prepare_for_decode call rebinds seq-lens tensors to new +1 objects without mutating the old ones."""