You should set the 'cls' property with 'panel-overflow-visible' value to let the panel has the 'overflow:visible' style.
<div data-options="region:'center'" cls="panel-overflow-visible" style="overflow:visible">
<table id="dg" data-options="header:'#invoices_header',singleSelect:true,border:false,fit:true,fitColumns:true,scrollbarSize:0,cls:'panel-overflow-visible'">
...
The example below works fine.
http://code.reloado.com/ecituq3/31/edit#preview