For period-select and year-select I found out "task" was missing:
Added this.form.task.value=\'\';
models\eurecap.php line 232
$listHTML = JHtml::_ ('select.genericlist', $options, 'month', 'class="inputbox" style="width: inherit onchange="this.form.task.value=\'\'; this.form.submit();" ', 'text', 'value', $selected);
line 242
$listHTML = JHtml::_ ('select.genericlist', $options, 'year', 'class="inputbox" style="width: inherit" onchange="this.form.task.value=\'\'; this.form.submit();" ', 'text', 'value', $selected);
I didn't figure out how to reset "task" when I click on a sorted header.
So sorting after export still gives the error...