diff --git a/apps/api/src/ldap/ldap.service.spec.ts b/apps/api/src/ldap/ldap.service.spec.ts
index f87628e..814c887 100644
--- a/apps/api/src/ldap/ldap.service.spec.ts
+++ b/apps/api/src/ldap/ldap.service.spec.ts
@@ -1627,6 +1627,36 @@ describe('LdapService.syncBoundGroupsForTenant — Rekonziliation gegen das Verz
     expect(second.groupsRenamed).toBe(0);
     expect(second.groupsDeleted).toBe(0);
   });
+
+  it('a hit whose cn/dn differ only in casing from the stored values is NOT a rename — no write, no groupsRenamed increment (WR-04, 16-REVIEW.md)', async () => {
+    // Simulates a domain-controller switch returning different casing for
+    // the same, unchanged AD group between two syncs — Priority Check 7
+    // ("sync twice over an unchanged AD state = no-op") must hold even
+    // then.
+    groups = [
+      {
+        id: 'g1',
+        tenantId: 't1',
+        name: 'Sales',
+        ldapDn: 'CN=Sales,DC=example,DC=com',
+        ldapObjectGuid: guidHex,
+        isDefault: false,
+      },
+    ];
+    mockSearch.mockResolvedValue({
+      searchEntries: [{ dn: 'cn=sales,dc=example,dc=com', cn: 'sales' }],
+    });
+
+    const result = makeResult();
+    await run(result);
+
+    expect(prisma.group.update).not.toHaveBeenCalled();
+    expect(result.groupsRenamed).toBe(0);
+    // The stored value is untouched — it is NOT rewritten to the
+    // differently-cased AD response either.
+    expect(groups[0].name).toBe('Sales');
+    expect(groups[0].ldapDn).toBe('CN=Sales,DC=example,DC=com');
+  });
 });
 
 describe('LdapService — AD group import (SC-1/SC-2, D-01/D-02)', () => {
diff --git a/apps/api/src/ldap/ldap.service.ts b/apps/api/src/ldap/ldap.service.ts
index df3d72d..ed42805 100644
--- a/apps/api/src/ldap/ldap.service.ts
+++ b/apps/api/src/ldap/ldap.service.ts
@@ -1308,8 +1308,27 @@ export class LdapService {
               : hit.dn;
           const dn = hit.dn;
 
-          if (name !== group.name || dn !== group.ldapDn) {
+          // WR-04 (16-REVIEW.md): the CHANGE CHECK is case-insensitive —
+          // only the DECISION "is this a rename" is normalized, never the
+          // value written below. AD returning the same cn/dn with different
+          // casing between two runs (e.g. after a domain-controller switch)
+          // must not look like a rename: that would break the idempotency
+          // guarantee (Priority Check 7 — sync twice over an unchanged AD
+          // state = no-op) and increment groupsRenamed / issue an update on
+          // every subsequent run. This is a plain lowercase compare, not
+          // full RFC 4514 DN canonicalization (per-attribute-type
+          // case-sensitivity rules, escaped-character normalization, etc.)
+          // — a pragmatic simplification, same uncertainty class as A1/A2 in
+          // RESEARCH.md, not verified against a real AD.
+          const nameChanged = name.toLowerCase() !== (group.name ?? '').toLowerCase();
+          const dnChanged =
+            dn.toLowerCase() !== (group.ldapDn ?? '').toLowerCase();
+
+          if (nameChanged || dnChanged) {
             try {
+              // The write below stores name/dn EXACTLY as the directory
+              // reports them, byte-for-byte — never the lowercased
+              // comparison values above. Group.name stays AD's, per D-03.
               await tenantPrisma.group.update({
                 where: { id: group.id },
                 data: { name, ldapDn: dn },