diff --git a/backends/ezdxf_backend.py b/backends/ezdxf_backend.py
index c36ad56..2e49151 100644
--- a/backends/ezdxf_backend.py
+++ b/backends/ezdxf_backend.py
@@ -4453,12 +4453,20 @@ class EzdxfBackend(AutoCADBackend):
             }
             if layer:
                 attribs["layer"] = layer
+            # `add_blockref` never checks the name, and `add_auto_attribs`
+            # silently skips autofill when `Insert.block()` resolves to None,
+            # so a typo'd name used to yield a dangling INSERT that dropped its
+            # attribute values and that `doc.audit()` later deletes. Refuse
+            # before writing, as COM's `InsertBlock` does for an unknown name.
+            if name not in self._doc.blocks:
+                raise ValueError(f"block {name!r} is not defined")
+            ref = msp.add_blockref(name, (float(x), float(y)), dxfattribs=attribs)
             if attributes:
-                ref = msp.add_auto_blockref(
-                    name, (float(x), float(y)), attributes, dxfattribs=attribs
-                )
-            else:
-                ref = msp.add_blockref(name, (float(x), float(y)), dxfattribs=attribs)
+                # `add_auto_blockref` wraps the INSERT in an anonymous *U block,
+                # so the returned handle names `*U1` and carries no ATTRIBs.
+                # `add_auto_attribs` attaches ATTRIBs to this INSERT for every
+                # ATTDEF the definition has; values for tags it lacks are ignored.
+                ref.add_auto_attribs({str(k): str(v) for k, v in attributes.items()})
             self._mark_dirty()
             return _entity_info_dxf(ref)
 
diff --git a/tests/test_block_insert_attributes.py b/tests/test_block_insert_attributes.py
new file mode 100644
index 0000000..59a69f7
--- /dev/null
+++ b/tests/test_block_insert_attributes.py
@@ -0,0 +1,55 @@
+"""block_insert(attributes=...) must reference the named block, not an anonymous wrapper.
+
+ezdxf's `add_auto_blockref` wraps the INSERT in an anonymous `*U` block. The
+handle it returns then reports block_name `*U1`, and `block_get_attributes`
+finds no ATTRIBs on it — an insert with attributes silently lost them.
+"""
+
+from __future__ import annotations
+
+import pytest
+
+pytestmark = pytest.mark.asyncio
+
+
+def _define_tagged_block(backend, name: str = "TB") -> None:
+    blk = backend._doc.blocks.new(name=name)
+    blk.add_line((0, 0), (10, 0))
+    blk.add_attdef("TAG", insert=(0, 3), text="", dxfattribs={"height": 2.5})
+
+
+async def test_insert_with_attributes_references_the_named_block(backend):
+    _define_tagged_block(backend)
+    ref = await backend.block_insert("TB", 10, 10, attributes={"TAG": "P-101"})
+
+    info = await backend.entity_get(ref.handle)
+    assert info.properties["block_name"] == "TB"
+    assert await backend.block_get_attributes(ref.handle) == {"TAG": "P-101"}
+    anonymous = [b.name for b in backend._doc.blocks if b.name.startswith("*U")]
+    assert anonymous == [], "no anonymous wrapper block may be created"
+
+
+async def test_insert_ignores_values_for_tags_the_block_does_not_define(backend):
+    _define_tagged_block(backend)
+    ref = await backend.block_insert("TB", 0, 0, attributes={"TAG": "V-1", "NOPE": "x"})
+    assert await backend.block_get_attributes(ref.handle) == {"TAG": "V-1"}
+
+
+async def test_insert_without_attributes_is_unchanged(backend):
+    _define_tagged_block(backend)
+    ref = await backend.block_insert("TB", 0, 0)
+    info = await backend.entity_get(ref.handle)
+    assert info.properties["block_name"] == "TB"
+    assert await backend.block_get_attributes(ref.handle) == {}
+
+
+@pytest.mark.parametrize("attributes", [{"TAG": "P-101"}, None], ids=["with-attrs", "no-attrs"])
+async def test_insert_of_undefined_block_is_refused_before_writing(backend, attributes):
+    # `add_blockref` never checks the name and `add_auto_attribs` skips autofill
+    # when the definition is missing, so a typo'd name used to return a handle
+    # whose attribute values were dropped and which `doc.audit()` later deletes.
+    before = len(list(backend._msp()))
+    with pytest.raises(ValueError, match="'NO_SUCH_BLOCK' is not defined"):
+        await backend.block_insert("NO_SUCH_BLOCK", 5, 5, attributes=attributes)
+    assert len(list(backend._msp())) == before, "a refused insert must not write"
+    assert [b.name for b in backend._doc.blocks if b.name == "NO_SUCH_BLOCK"] == []