1.control panel-->custom field
2.add a custom field named "test" for bookmarks and type is "selection of Integer values".
3.edit the custom field,input some integers as default value and make sure "display type" is "check box".save
4.add a new bookmark
5.input some value for the bookmark,and make sure more than two options be selected.save
6.click the bookmark ,you will see just first selected value has been saved ,another be lost.