Ellipsis renderer not working with mjoin?

The following is not working for Ellipisis renderer on column 4 'unit outcome' which is using mjoin data. Not sure where the problem is though. The data from mjoin is wrapped in para tags. I can get ellipsis applied to other columns in this table no problem.

var table = $( '#unit_table' ).DataTable( {
                responsive: true,
                columnDefs: [ {
                    targets: 4,
                    render: $.fn.dataTable.render.ellipsis( 10, true )
                } ],
                ajax: "program_data/unit_data.php",
                dom: "Blfrtip",
                columns: [ {
                    data: "unit.unit_code"
                }, {
                    data: "unit.unit_name"
                }, {
                    data: "unit.points"
                }, {
                    data: "year.year_name"
                },{
                    data: "unit_outcome",
                    render: "[; ].unit_outcome"
                }, {
                    data: "unit.modified"
                }, {
                    data: "unit.modified_by"
                } ],
                select: {
                    style: 'os',
                    selector: 'td:first-child'
                },
                buttons: [ ]
            } );