diff --git a/frontend/js/views/layout-editor.js b/frontend/js/views/layout-editor.js
index 33bfe5c..51f4900 100644
--- a/frontend/js/views/layout-editor.js
+++ b/frontend/js/views/layout-editor.js
@@ -293,15 +293,21 @@ async function renderEditor(container, layoutId) {
 
   document.getElementById('saveLayoutBtn').onclick = async () => {
     try {
-      for (const z of layout.zones || []) {
-        await API(`/layouts/${layoutId}/zones/${z.id}`, { method: 'DELETE' });
-      }
-      for (const z of zones) {
-        await API(`/layouts/${layoutId}/zones`, { method: 'POST', body: JSON.stringify(z) });
-      }
+      // Single atomic update: send the full zone set and the server replaces them
+      // exactly. The old per-zone delete-then-add loop could accumulate zones
+      // (and regenerated every zone id each save). Keep each zone's id so
+      // device->zone assignments survive.
+      const updated = await API(`/layouts/${layoutId}`, {
+        method: 'PUT',
+        body: JSON.stringify({ zones }),
+      });
+      if (updated && updated.error) { showToast(updated.error, 'error'); return; }
+      layout = updated;
+      zones = layout.zones || [];
+      selectedZone = null;
       showToast(t('layout.toast.saved'), 'success');
-      layout = await API(`/layouts/${layoutId}`);
-      zones = layout.zones;
+      renderZones();
+      updateProperties();
     } catch (err) {
       showToast(err.message, 'error');
     }
diff --git a/server/db/database.js b/server/db/database.js
index 5169016..84c4f73 100644
--- a/server/db/database.js
+++ b/server/db/database.js
@@ -719,6 +719,40 @@ function pruneScreenshots(deviceId) {
   `).run(deviceId, deviceId);
 }
 
+// De-duplicate built-in template zones. A prior layout-editor save regenerated
+// every zone id on save; schema.sql's INSERT OR IGNORE then re-seeded the
+// canonical zone on the next boot, so template layouts accumulated positional
+// duplicates (e.g. a 2-zone split template grew to 4+). For each position in a
+// template, keep ONE zone, preferring the canonical seeded id (the built-in
+// template zones use 'z-...' ids; bug copies are uuids) so schema.sql's re-seed
+// stays an idempotent no-op; tiebreak by earliest rowid. One-time; the atomic
+// id-preserving save prevents recurrence.
+try {
+  const DEDUPE_ID = 'dedupe_template_zones_v1';
+  if (!db.prepare('SELECT 1 FROM schema_migrations WHERE id = ?').get(DEDUPE_ID)) {
+    const removed = db.prepare(`
+      DELETE FROM layout_zones WHERE id IN (
+        SELECT z.id FROM layout_zones z
+        JOIN layouts l ON l.id = z.layout_id
+        WHERE l.is_template = 1 AND EXISTS (
+          SELECT 1 FROM layout_zones z2
+          WHERE z2.layout_id = z.layout_id AND z2.id != z.id
+            AND z2.x_percent = z.x_percent AND z2.y_percent = z.y_percent
+            AND z2.width_percent = z.width_percent AND z2.height_percent = z.height_percent
+            AND (
+              -- z2 is canonical and z is not -> keep z2, drop z
+              (z2.id LIKE 'z-%' AND z.id NOT LIKE 'z-%')
+              -- same canonical-ness -> keep the earliest, drop the rest
+              OR ((CASE WHEN z2.id LIKE 'z-%' THEN 1 ELSE 0 END) = (CASE WHEN z.id LIKE 'z-%' THEN 1 ELSE 0 END) AND z2.rowid < z.rowid)
+            )
+        )
+      )
+    `).run().changes;
+    if (removed > 0) console.log(`[migrate] removed ${removed} duplicate template zone(s)`);
+    db.prepare('INSERT OR IGNORE INTO schema_migrations (id) VALUES (?)').run(DEDUPE_ID);
+  }
+} catch (e) { console.error('[migrate] template-zone dedupe failed:', e.message); }
+
 // #37: fail fast (loud) if migrations left the DB missing schema the code needs.
 const { verifyAndRepairSchema } = require('../lib/schema-check');
 verifyAndRepairSchema(db);
diff --git a/server/routes/layouts.js b/server/routes/layouts.js
index 7653aa6..c3e1595 100644
--- a/server/routes/layouts.js
+++ b/server/routes/layouts.js
@@ -116,10 +116,32 @@ router.put('/:id', (req, res) => {
   if (!layout) return;
   if (layout.is_template && !PLATFORM_ROLES.includes(req.user.role)) return res.status(403).json({ error: 'Cannot edit templates' });
 
-  const { name, width, height } = req.body;
-  if (name) db.prepare('UPDATE layouts SET name = ?, updated_at = strftime(\'%s\',\'now\') WHERE id = ?').run(name, req.params.id);
-  if (width) db.prepare('UPDATE layouts SET width = ? WHERE id = ?').run(width, req.params.id);
-  if (height) db.prepare('UPDATE layouts SET height = ? WHERE id = ?').run(height, req.params.id);
+  const { name, width, height, zones } = req.body;
+  const txn = db.transaction(() => {
+    if (name) db.prepare('UPDATE layouts SET name = ?, updated_at = strftime(\'%s\',\'now\') WHERE id = ?').run(name, req.params.id);
+    if (width) db.prepare('UPDATE layouts SET width = ? WHERE id = ?').run(width, req.params.id);
+    if (height) db.prepare('UPDATE layouts SET height = ? WHERE id = ?').run(height, req.params.id);
+
+    // Atomic zone replace: the editor sends the FULL desired set, so the layout
+    // ends up with EXACTLY those zones - no accumulation from a per-zone
+    // delete/add loop. Reuse each zone's id when supplied so device->zone
+    // assignments survive an edit (a fresh uuid per save would orphan them).
+    if (Array.isArray(zones)) {
+      db.prepare('DELETE FROM layout_zones WHERE layout_id = ?').run(req.params.id);
+      const stmt = db.prepare(`
+        INSERT INTO layout_zones (id, layout_id, name, x_percent, y_percent, width_percent, height_percent, z_index, zone_type, fit_mode, background_color, sort_order)
+        VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+      `);
+      zones.forEach((z, i) => {
+        stmt.run(z.id || uuidv4(), req.params.id, z.name || `Zone ${i + 1}`,
+          z.x_percent || 0, z.y_percent || 0, z.width_percent || 100, z.height_percent || 100,
+          z.z_index || 0, z.zone_type || 'content', z.fit_mode || 'contain',
+          z.background_color || '#000000', i);
+      });
+      db.prepare('UPDATE layouts SET updated_at = strftime(\'%s\',\'now\') WHERE id = ?').run(req.params.id);
+    }
+  });
+  txn();
 
   const updated = db.prepare('SELECT * FROM layouts WHERE id = ?').get(req.params.id);
   updated.zones = db.prepare('SELECT * FROM layout_zones WHERE layout_id = ? ORDER BY sort_order').all(req.params.id);