It looks like colspan for the group headers is derived from count(@columns).
If @colums is missing it becomes 0, but the backend code displays all columns
of the issue class.

Changing:


  <th tal:attributes="colspan python:len(request.columns)" class="group">

to an arbitrary large number:

  <th tal:attributes="colspan python:len(request.columns) or 100" class="group">

solves the issue. I don't think it has any bad effects.

Comments?