No Scrollbars in GWT Flextable

No Scrollbars in GWT Flextable

I am creating a flextable and adding cells in it dynamically. Flextable is
inside scrollpanel but scrollbars never come vertically. They always come
horizontally/
<g:ScrollPanel ui:field='toppanel'>
</g:ScrollPanel>
Flextable is added in this Scrollpanel dynamically as toppanel.add(stutable);