After deleting a node it is still in get checked array as false. This means if you delete and then need to check if more than one node is checked, one needs to iterate over checked array and remove false's
inst.get_checked(true).length ; // this is x
inst.check_node('2');
inst.delete_node('2');
inst.get_checked(true).length ; // this is x+1 should be x
fiddle: fiddle
After deleting a node it is still in get checked array as false. This means if you delete and then need to check if more than one node is checked, one needs to iterate over checked array and remove false's