diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8f71c20e7..30afa5e34 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -333,6 +333,12 @@ loading. A port that reports `1.2` does not know that vocabulary; upgrade every
 
 ### Fixed
 
+- **TypeScript: a derived flattened `field.object` no longer produces flat member keys (#524
+  follow-up).** A flattened field that carries an `origin.*` owns no column (the Drizzle table and
+  `meta migrate` skip it), but the flat keys (`shipToStreet`) still appeared in the read, create and
+  update schemas, the filter and sort allowlists, the OpenAPI bodies and the form, so a write dropped
+  them silently. The flattened member expansion now skips a derived parent, so every generated
+  surface agrees with the table.
 - **TypeScript: Drizzle now binds a `field.object` with `@storage: flattened` to its member columns
   (#524).** The generator used to emit one `jsonb` column named for the field, while `meta migrate`
   creates one column per member of the value object and none for the field, so every generated
diff --git a/docs/features/field-types.md b/docs/features/field-types.md
index d04de99e8..f267c7b2c 100644
--- a/docs/features/field-types.md
+++ b/docs/features/field-types.md
@@ -365,8 +365,9 @@ function `meta migrate` uses. The Row and Insert types, the Zod schemas, the fil
 allowlists, the OpenAPI parameters and the form and grid generators all expose those flat keys;
 a client reads and writes `addressStreet`, not a nested `address` object. A flattened field
 declared on a TPH subtype keeps one column named for the field, as `meta migrate` creates it.
-A flattened field on a write-through entity is refused at `meta gen`
-([source-kinds.md](source-kinds.md)).
+A flattened field that carries an `origin.*` is derived: it owns no columns, so it exposes no flat
+keys in any of those surfaces, and a write cannot set them. A flattened field on a write-through
+entity is refused at `meta gen` ([source-kinds.md](source-kinds.md)).
 
 ```ts
 // generated/acme/blog/Author.ts
diff --git a/server/typescript/packages/codegen-ts/src/flattened.ts b/server/typescript/packages/codegen-ts/src/flattened.ts
index 9c6ebe03b..d4313158d 100644
--- a/server/typescript/packages/codegen-ts/src/flattened.ts
+++ b/server/typescript/packages/codegen-ts/src/flattened.ts
@@ -51,6 +51,9 @@ export function isFlattenedObjectField(field: MetaField): boolean {
 /** The members of a flattened field, or undefined when it is not flattened (or names no value object). */
 export function flattenedMembersOf(field: MetaField, strategy: ColumnNamingStrategy): FlattenedMember[] | undefined {
   if (!isFlattenedObjectField(field)) return undefined;
+  // A derived (origin-bearing) field is materialized on the read side and owns no column, so its
+  // members are no columns either; drizzle-schema and migrate's expected schema skip it too.
+  if (field.isDerived()) return undefined;
   const valueObject = refTarget(field, FIELD_ATTR_OBJECT_REF);
   if (valueObject === undefined || !isMetaObject(valueObject)) return undefined;
   // ADR-0039: effective fields — members inherited via extends are columns too (as migrate does).
diff --git a/server/typescript/packages/codegen-ts/test/flattened-storage-e2e.test.ts b/server/typescript/packages/codegen-ts/test/flattened-storage-e2e.test.ts
index 408125458..5262d941e 100644
--- a/server/typescript/packages/codegen-ts/test/flattened-storage-e2e.test.ts
+++ b/server/typescript/packages/codegen-ts/test/flattened-storage-e2e.test.ts
@@ -196,6 +196,51 @@ describe("flattened storage: a derived value-object member keeps its column", ()
   });
 });
 
+describe("flattened storage: a derived flattened parent has no member keys or columns", () => {
+  const DERIVED_PARENT = JSON.stringify({
+    "metadata.root": { package: "acme", children: [
+      { "object.value": { name: "Address", children: [
+        { "field.string": { name: "street" } },
+        { "field.string": { name: "city", "@filterable": true } },
+      ] } },
+      { "object.entity": { name: "Owner", children: [
+        { "source.rdb": { "@table": "owners" } },
+        { "field.long": { name: "id" } },
+        { "field.object": { name: "home", "@objectRef": "Address", "@storage": "flattened" } },
+        { "identity.primary": { name: "pk", "@fields": "id", "@generation": "increment" } },
+      ] } },
+      { "object.entity": { name: "Parcel", children: [
+        { "source.rdb": { "@table": "parcels", "@role": "primary" } },
+        { "source.rdb": { "@kind": "view", "@view": "v_parcels", "@role": "replica" } },
+        { "field.long": { name: "id" } },
+        { "field.string": { name: "ref" } },
+        { "field.long": { name: "ownerId" } },
+        { "field.object": { name: "shipTo", "@objectRef": "Address", "@storage": "flattened", children: [
+          { "origin.passthrough": { "@from": "Owner.home", "@via": "Parcel.owner" } },
+        ] } },
+        { "identity.primary": { name: "pk", "@fields": "id", "@generation": "increment" } },
+        { "identity.reference": { name: "ownerRef", "@fields": "ownerId", "@references": "Owner" } },
+        { "relationship.association": { name: "owner", "@cardinality": "one", "@objectRef": "Owner" } },
+      ] } },
+    ] },
+  });
+
+  test("no flat keys on the surface, in the schemas or allowlists, and no Drizzle member columns", async () => {
+    const { root, errors } = await new MetaDataLoader({ strict: true }).load([new InMemoryStringSource(DERIVED_PARENT, { id: "dp.json" })]);
+    expect(errors).toEqual([]);
+    const parcel = root.findObject("Parcel")!;
+    expect(flatSurfaceFields(parcel).map((f) => f.name)).toEqual(["id", "ref", "ownerId", "shipTo"]);
+
+    const outDir = await generate(root, "postgres", [entityFile(), queriesFile()], tmpdir());
+    const entity = readFileSync(allTs(outDir).find((f) => f.endsWith("Parcel.ts"))!, "utf8");
+    const table = entity.slice(entity.indexOf("Table(\"parcels\""), entity.indexOf("});", entity.indexOf("Table(\"parcels\"")));
+    expect([...table.matchAll(/^\s+\w+: \w+\("([^"]+)"/gm)].map((m) => m[1]!).sort()).toEqual(["id", "owner_id", "ref"]);
+    for (const file of allTs(outDir).filter((f) => /Parcel[.\w]*\.ts$/.test(f))) {
+      expect(readFileSync(file, "utf8")).not.toMatch(/shipTo(Street|City)|ship_to_/);
+    }
+  });
+});
+
 describe("flattened storage: agent/ui.md reports the flat keys with their flags", () => {
   test("a filterable member's row is marked filterable and sortable", async () => {
     const page = renderAgentUiPage(await load());