private void syntaxEditor_Loaded(object sender, RoutedEventArgs e)
{
	var buttons = this.syntaxEditor.ChildrenOfType<RadToggleButton>();
	var matchCaseButton = buttons.FirstOrDefault(x => x.Name == "PART_MatchCaseButton");
	var matchWordButton = buttons.FirstOrDefault(x => x.Name == "PART_MatchWordButton");
	var useRegularExpressionsButton = buttons.FirstOrDefault(x => x.Name == "PART_UseRegularExpressionsButton");

	matchCaseButton.ToolTip = CreateToolTip("SyntaxEditor_MatchCase"); // these are custom localization resource keys that should be manually defined by the developer that uses this solution
	matchWordButton.ToolTip = CreateToolTip("SyntaxEditor_MatchWord");
	useRegularExpressionsButton.ToolTip = CreateToolTip("SyntaxEditor_UseRegularExpressions");
}

private static ToolTip CreateToolTip(string resourceKey)
{
	var toolTip = new ToolTip();
	toolTip.Content = LocalizationManager.Manager.GetStringOverride(resourceKey);
	return toolTip;
}

The exception message is the following: System.ArgumentException: 'The value '102' is not a valid value for the enum 'FilterOperator'.'

To work this around, avoid using mixed typed values in the ItemsSource.