ngModelAttrs - options-disabled is not disabling the select elements

i am trying to disable the select options based on the selected group so that same group should not be selectable in further dropdowns.. but ngModelAttrs is not working as expected with options-disabled

belows is the jsbin which shows the issue
http://jsbin.com/duzuce/edit?js,output

disabledGroups already holds the "Vehicle Loans" group which mean by default Vehicle Loans should be disabled in all the three dropdown which is not the case.. and based on the selection in first select.. corresponding groupd should get disabled in further choice lists

Any help would be appreciated