diff --git a/qwen3_6_scripts/mamba_cache.py b/qwen3_6_scripts/mamba_cache.py
index 7537b9e9..8a3795f1 100644
--- a/qwen3_6_scripts/mamba_cache.py
+++ b/qwen3_6_scripts/mamba_cache.py
@@ -70,10 +70,15 @@ class MambaCacheManager:
         return tuple(buffer[:, :batch_size] for buffer in self.mamba_cache)
 
     def _swap_mamba_cache(self, from_index: int, to_index: int):
+        # CCCL DeviceCopy::Batched uses separate src/dst buffers — never
+        # in-place scatter. PyTorch advanced indexing assignment
+        # cache[:, [a,b]] = cache[:, [b,a]] has undefined evaluation order.
+        # Use explicit temp clone for correctness.
         assert len(self.mamba_cache) > 0
         for cache_t in self.mamba_cache:
-            cache_t[:, [to_index,from_index]] = \
-             cache_t[:, [from_index,to_index]]
+            tmp = cache_t[:, from_index].clone()
+            cache_t[:, from_index].copy_(cache_t[:, to_index])
+            cache_t[:, to_index].copy_(tmp)
 
     def _copy_mamba_cache(self, from_index: int, to_index: int):
         assert len(self.mamba_cache) > 0