When selecting "Display the "Add more hours" link" the colspan on the table header is wrong

In theme_office_hours_multiple_values() there is a hardcoded colspan => 1 in the header definition. However, when one selects "Display the "Add more hours" link" one the field the link is outputted in an extra column and then the header doesn't span the whole table anymore. It still displays kind of correctly in most browsers except IE.

The colspan value should be dependent on the options chosen for the field.