We dropped using this widget, mostly because of performance issues, and use a reference set selector instead with a listview on the select page. User experience is virtually the same: a popup with checkboxes and search functionality. To show 'object X selected', '3 selected', 'all selected' etc we use the custom string widget and some custom styling.
As a workaround you can use persistable entities and make sure that you never commit them, or dispose them afterwards.
Hope this helps