form_checkbox and set_checkbox

[eluser]froginvasion[/eluser]
I'm trying to use both functions in one, as it would make it easier than just writing plain HTML tags. The code that causes me trouble is this one:

Code:

<fieldset>
    <legend>locaties</legend>
    &lt;?php echo form_checkbox('locatie','oudenaarde', set_checkbox('locatie','oudenaarde'));?&gt;3-7-2011 te Oudenaarde <br />
    &lt;?php echo form_checkbox('locatie','arendonk', set_checkbox('locatie','arendonk'));?&gt;31-7-2011 Arendonk<br />
    &lt;?php echo form_checkbox('locatie','westdonk', set_checkbox('locatie','westdonk'));?&gt;11-09-2011 Westhoek – MERKEN<br />
</fieldset>

It should repopulate the checkboxes at validation, but it only sets back one of them, and never more than one. But I don't know why...