If I had correctly understood your scenario - the DropDown element of the widget cannot be displayed, when the dropdownlist is placed within table cell. If this is correct, the issue seems to be related with some custom css styling applied to the dropdown or if this element inherits some styles which are preventing it from showing.
In order to efficiently assist you in overcoming this issue, we would need to observe your proper implementation and styling, so we could pin down the exact reason for it. It would be great if you could isolate the issue in a dojo example
and send it to us, so we could revise it.