Replicated only when Orientation=Vertical. The problem seems to be the _responsiveCheck function of Toolbar\Views\LiteView.js called from the _repaint method of the same file. screencast: https://www.screencast.com/t/SF5b1KZR7pIp screenshot before/after https://www.screencast.com/t/KG645ZgX Workaround: calling toolbar.get_view()._showAllHiddenItems(); after adding programmatically the buttons.