gentable cell padding

Does anyone know how to remove default cell padding in a gentable? If I insert a table in my SGML file and remove the top and bottom padding, I get this:

<table>
<title></title>
<tgroup cols="2">

<colspec colname="col1">
<colspec colname="col2">
<tbody>
<row>
<entry></entry>
<entry></entry>
</row>
<row>
<entry></entry>
<entry></entry>
</row>
</tbody>
</tgroup>
</table>

but if I paste that into a usetext, I get unbalanced tag errors. I tried adding cbmarg="0.00pt" ctmarg="0.00pt" to the tgroup (and row, table, etc.) and that doesn't do anything. I wonder if this might be a DTD issue.