diff --git a/adminfront/src/features/users/UserDetailPage.tsx b/adminfront/src/features/users/UserDetailPage.tsx
index 6db94a92..e526c619 100644
--- a/adminfront/src/features/users/UserDetailPage.tsx
+++ b/adminfront/src/features/users/UserDetailPage.tsx
@@ -139,7 +139,9 @@ function TenantMetadataFields({
   );
 }
 
-type UserFormValues = UserUpdateRequest & { metadata: Record<string, any> };
+type UserFormValues = Omit<UserUpdateRequest, "metadata"> & {
+  metadata: Record<string, Record<string, any>>;
+};
 
 function UserDetailPage() {
   const params = useParams<{ id: string }>();
@@ -299,7 +301,20 @@ function UserDetailPage() {
   const onSubmit = (data: UserFormValues) => {
     setError(null);
     setSuccessMsg(null);
-    mutation.mutate(data);
+
+    // Filter out undefined/null/empty strings from metadata
+    const cleanMetadata = Object.fromEntries(
+      Object.entries(data.metadata).map(([tenantId, fields]) => {
+        const cleanFields = Object.fromEntries(
+          Object.entries(fields).filter(
+            ([_, v]) => v !== undefined && v !== null && v !== "",
+          ),
+        );
+        return [tenantId, cleanFields];
+      }),
+    );
+
+    mutation.mutate({ ...data, metadata: cleanMetadata });
   };
 
   const handleDelete = () => {
diff --git a/backend/internal/handler/user_handler.go b/backend/internal/handler/user_handler.go
index 40d101f1..112b95bb 100644
--- a/backend/internal/handler/user_handler.go
+++ b/backend/internal/handler/user_handler.go
@@ -1194,15 +1194,28 @@ func (h *UserHandler) UpdateUser(c *fiber.Ctx) error {
 	}
 
 	// For namespaced metadata, we don't delete everything, we merge.
-	// But we should remove legacy flat traits that are not in the new req.Metadata if we want strict sync.
-	// For now, let's just merge.
 	for k, v := range req.Metadata {
 		if !coreTraits[k] {
-			traits[k] = v
+			// Ensure we are merging maps (tenant namespaces) correctly, not overwriting with slices
+			if incomingMap, ok := v.(map[string]any); ok {
+				if existingMap, ok := traits[k].(map[string]interface{}); ok {
+					for subK, subV := range incomingMap {
+						existingMap[subK] = subV
+					}
+					traits[k] = existingMap
+				} else {
+					traits[k] = incomingMap // New namespace
+				}
+			} else {
+				traits[k] = v // Fallback for flat metadata
+			}
 		}
 	}
 
 	state := normalizeKratosState(req.Status)
+
+	slog.Info("[UpdateUser] Calling Kratos UpdateIdentity", "userID", userID, "traits", traits, "state", state)
+
 	updated, err := h.KratosAdmin.UpdateIdentity(c.Context(), userID, traits, state)
 	if err != nil {
 		return errorJSON(c, fiber.StatusInternalServerError, err.Error())