Modal title appearing after close ('x') button

I've recently made changes to my Editor configuration and the following behaviour has popped up:

<div data-dte-e="head" class="DTE_Header modal-header">
    <button class="close">x</button>
    <div class="DTE_Header_Content"><h5 class="modal-title">New record</h5></div>
</div>

i.e. in the Editor modal dialog, the title appears to the right of the close button.

I initialize the Create button as follows:

new $.fn.dataTable.Buttons( datatable, {
    buttons: [
        {
            text: 'New...',
            action: function ( e, dt, node, config ) {
                  
                bb.editor.create(
                    {
                        submitOnReturn: false,
                        title: '<h5 class="modal-title">New record</h5>'
                    }
                );
            }
         }
     ]
} );

datatable.buttons().container()
    .appendTo( $('.buttonSlot', datatable.table().container() ) );

Allan, I can supply a page link and password if you need it.

Thanks in advance.