diff --git a/client/internal/profilemanager/config_optional_fields_test.go b/client/internal/profilemanager/config_optional_fields_test.go
new file mode 100644
index 000000000..9b74e2217
--- /dev/null
+++ b/client/internal/profilemanager/config_optional_fields_test.go
@@ -0,0 +1,131 @@
+package profilemanager
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"reflect"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+// optionalBoolFields lists the *bool fields of Config by name, derived from the
+// type so a field added later is covered without touching these tests.
+func optionalBoolFields() []string {
+	pointerToBool := reflect.TypeOf((*bool)(nil))
+
+	var fields []string
+	configType := reflect.TypeOf(Config{})
+	for i := range configType.NumField() {
+		field := configType.Field(i)
+		if field.Type == pointerToBool && field.Tag.Get("json") != "-" {
+			fields = append(fields, field.Name)
+		}
+	}
+	return fields
+}
+
+func requireNoUnsetOptionalBool(t *testing.T, config *Config, context string) {
+	t.Helper()
+
+	value := reflect.ValueOf(*config)
+	for _, name := range optionalBoolFields() {
+		require.False(t, value.FieldByName(name).IsNil(),
+			"%s left %s unset, so its readers have to invent a default and a diff of it compares presence instead of value", context, name)
+	}
+}
+
+// An optional bool must not be tristate. While one can be nil, true or false,
+// every reader has to invent the meaning of nil, and — the reason this test
+// exists — a diff of the config ends up comparing presence rather than value:
+// that is what made the update-settings gate refuse `netbird up` for a client
+// restating its own defaults. apply() is where a config becomes complete, so
+// the invariant belongs to it: no *bool may come out of apply() unset.
+func TestApplyLeavesNoOptionalBoolUnset(t *testing.T) {
+	require.NotEmpty(t, optionalBoolFields(), "the invariant is only meaningful while Config has optional bools")
+
+	t.Run("a config built from scratch", func(t *testing.T) {
+		config := newConfigSkeleton()
+		_, err := config.apply(ConfigInput{})
+		require.NoError(t, err)
+
+		requireNoUnsetOptionalBool(t, config, "apply on a new config")
+	})
+
+	t.Run("a config file that predates every optional field", func(t *testing.T) {
+		path := filepath.Join(t.TempDir(), "legacy.json")
+		require.NoError(t, os.WriteFile(path, []byte(`{"WgIface":"wt0"}`), 0o600))
+
+		config, err := GetExistingConfig(path)
+		require.NoError(t, err)
+
+		requireNoUnsetOptionalBool(t, config, "a read of a legacy config")
+	})
+
+	t.Run("a config file that stores them as null", func(t *testing.T) {
+		path := filepath.Join(t.TempDir(), "null.json")
+		_, err := UpdateOrCreateConfig(ConfigInput{ConfigPath: path})
+		require.NoError(t, err)
+		unsetOnDisk(t, path, optionalBoolFields()...)
+
+		config, err := GetExistingConfig(path)
+		require.NoError(t, err)
+
+		requireNoUnsetOptionalBool(t, config, "a read of a config storing nulls")
+	})
+}
+
+// The same invariant on disk: what a write leaves in the file is what the next
+// client to read it starts from, so no write may store a null.
+func TestNoWriteStoresAnUnsetOptionalBool(t *testing.T) {
+	requireNoNullOnDisk := func(t *testing.T, path string, context string) {
+		t.Helper()
+
+		raw, err := os.ReadFile(path)
+		require.NoError(t, err)
+
+		var stored map[string]json.RawMessage
+		require.NoError(t, json.Unmarshal(raw, &stored))
+
+		for _, name := range optionalBoolFields() {
+			value, present := stored[name]
+			require.True(t, present, "%s did not store %s at all", context, name)
+			require.NotEqual(t, "null", string(value), "%s stored %s as null", context, name)
+		}
+	}
+
+	t.Run("UpdateOrCreateConfig", func(t *testing.T) {
+		path := filepath.Join(t.TempDir(), "created.json")
+		_, err := UpdateOrCreateConfig(ConfigInput{ConfigPath: path, ManagementURL: DefaultManagementURL})
+		require.NoError(t, err)
+
+		requireNoNullOnDisk(t, path, "UpdateOrCreateConfig")
+	})
+
+	t.Run("UpdateConfig over a config storing nulls", func(t *testing.T) {
+		path := filepath.Join(t.TempDir(), "stored.json")
+		_, err := UpdateOrCreateConfig(ConfigInput{ConfigPath: path})
+		require.NoError(t, err)
+		unsetOnDisk(t, path, optionalBoolFields()...)
+
+		_, err = UpdateConfig(ConfigInput{ConfigPath: path, ManagementURL: "https://mgmt.example.com"})
+		require.NoError(t, err)
+
+		requireNoNullOnDisk(t, path, "UpdateConfig")
+	})
+
+	// Renaming used to copy the file back through a bare Unmarshal, which
+	// preserved the nulls a pre-fix client had written.
+	t.Run("RenameProfile", func(t *testing.T) {
+		withTestSM(t, func(sm *ServiceManager, username string) {
+			created, err := sm.AddProfile("work", username)
+			require.NoError(t, err)
+			unsetOnDisk(t, created.Path, optionalBoolFields()...)
+
+			require.NoError(t, sm.RenameProfile(created.ID, username, "office"))
+
+			requireNoNullOnDisk(t, created.Path, "RenameProfile")
+		})
+	})
+}
diff --git a/client/internal/profilemanager/service.go b/client/internal/profilemanager/service.go
index ec287f01a..26b1d58fe 100644
--- a/client/internal/profilemanager/service.go
+++ b/client/internal/profilemanager/service.go
@@ -356,17 +356,17 @@ func (s *ServiceManager) RenameProfile(id ID, username string, newName string) e
 		return ErrProfileNotFound
 	}
 
-	data, err := os.ReadFile(target.Path)
+	// Through the reader, not a bare Unmarshal: this was the one write that
+	// skipped apply(), so it copied back whatever the file held — including an
+	// optional field left unset, which every other write resolves to its
+	// default. Renaming a profile is a poor place to leave that behind.
+	cfg, err := GetExistingConfig(target.Path)
 	if err != nil {
-		return err
-	}
-	var cfg Config
-	if err := json.Unmarshal(data, &cfg); err != nil {
-		return err
+		return fmt.Errorf("read profile config: %w", err)
 	}
 	cfg.Name = displayName
 
-	if err := util.WriteJson(context.Background(), target.Path, cfg); err != nil {
+	if err := WriteOutConfig(target.Path, cfg); err != nil {
 		return fmt.Errorf("failed to write profile name: %w", err)
 	}
 	return nil