I'm trying setup remote combobox with multiSelect in modern toolkit 7.1 like this:

  xtype: 'combobox',
  minChars: 3,
  name: 'articles_test',
  label: 'Articles',
  displayField: 'article_id',
  itemTpl: '<strong>{article_id}</strong> - {article_text}',
  valueField: 'article_text',
  triggerAction: 'query',
  queryMode: 'remote',
  placeholder: 'Search',
  forceSelection: true,
  hideTrigger: true,
  multiSelect: true,
  store: {
    model: 'Myapp.model.mytitles',
    autoLoad: false,
    remoteSort: true,
    remoteFilter: true,
    pageSize: 0
  labelWidth: 300
In remote store I have for example 1000 articles. When I search in combobox, remote store return 10 and I select one of these. If I search anoter article in same combobox, remote store return different range of articles and first one selected article is lost. I can't select more items from different ranges of articles. Is not usable list all 1000 articles at once. In classics toolkit this works.
What I have wrong?
Thank you.