Fix stale dotted-key prefix when replacing a table value with a plain dict

CHANGELOG.md

@@ -28,6 +28,7 @@
 - Fix `comment()` producing invalid TOML for a multiline string by prefixing every line with `#`, not just the first. ([#449](https://github.com/python-poetry/tomlkit/issues/449))
 - Fix the separator comma being swallowed by a trailing comment when appending a key to a multiline inline table, leaving the new key without a separator so the result no longer round-trips. ([#512](https://github.com/python-poetry/tomlkit/issues/512))
 - Fix a `KeyAlreadyPresent` error when parsing or accessing an out-of-order table whose array-of-tables elements are split across the table's parts. ([#505](https://github.com/python-poetry/tomlkit/issues/505))
+- Fix a stale dotted-key prefix when replacing a dotted-key table value with a plain dict, where ``fruit.apple = true`` followed by ``doc['fruit'] = {'a': 1}`` would render a ``[fruit]`` header followed by the wrongly dotted ``fruit.a = 1`` instead of ``a = 1``. ([#524](https://github.com/python-poetry/tomlkit/issues/524))
 
 ## [0.15.0] - 2026-05-10
 

tests/test_items.py

@@ -1236,6 +1236,18 @@ def test_serialize_table_with_dotted_key() -> None:
     assert parent.as_string() == "[a]\nb.c = 1\n"
 
 
+def test_replacing_dotted_key_table_clears_prefix() -> None:
+    """Replacing a dotted-key table with a plain dict should not carry
+    over the dotted prefix to the new children (#524)."""
+    doc = parse("fruit.apple = true\n")
+    doc["fruit"] = {"a": 1}
+    rendered = doc.as_string()
+    assert rendered == "[fruit]\na = 1\n"
+    # Round-trip
+    doc2 = parse(rendered)
+    assert doc2["fruit"]["a"] == 1
+
+
 def test_not_showing_parent_header_for_super_table() -> None:
     doc = api.document()
 

tomlkit/container.py

@@ -829,6 +829,7 @@ def _replace_at(
                 new_key = SingleKey(new_key)
             else:  # Inherit the sep of the old key
                 new_key = k
+                new_key._dotted = False  # Reset dotted heritage on full replacement
 
         del self._map[k]
         self._map[new_key] = idx