PrimeNG Drag and Drop not working without adding style class ui-helper-clearfix

I am making use of PrimeNG and Angular 8. The code snippet is as follows -

<div class="p-col-12 p-md-6 p-col-nogutter drag-column">
        <div *ngFor="let doc of availableDocs" class="ui-helper-clearfix">
            <div class="ui-g-12 ui-md-4" pDraggable="docs" (onDragStart)="dragStart($event, doc)"
                (onDragEnd)="dragEnd($event)">
                <p-panel [header]="doc.title" [style]="{'text-align':'center'}">
                    <img src="assets/images/{{doc.extension}}.png">
                </p-panel>
            </div>
        </div>
    </div>

If in above code we remove the class ui-helper-clearfix, then the image cannot be dragged. But in documentation no such requirement is mentioned. Can this be done without ui-helper-clearfix. Or some other solution as it is not the layout i want.