Tab breaks sorting in Grid

[donnysim]

I have a grid with fields:

'fields' => array(
            array(
                'label' => 'First',
                'type' => 'Tab',
                'preview' => false
            ),
            array(
                'field' => 'lang',
                'field_ref' => 'ref',
                'label' => 'Languages',
                'type' => 'Plugin\ReQ_Faq\Grid\Field\LanguageBar',
                'target' => array('title', 'content')
            ),
            array(
                'field' => 'title',
                'label' => 'Title',
                'type' => 'Text'
            ),
            array(
                'label' => 'Second',
                'type' => 'Tab',
                'preview' => false
            ),
            array(
                'field' => 'content',
                'label' => 'Content',
                'type' => 'RichText'
            )
        )

If I want to sort by column it throws undefined index "field" error. If I add field => '' to the first tab, I can sort by columns until the second tab. If I want to sort by content, I'd get the same error unless I add field to the second tab.

[maskas]

Looking